## WBBSE Class 10 Geography Solutions Chapter 2.3 Heat, Temperature and Global Warming

Detailed explanations in West Bengal Board Class 10 Geography Book Solutions Chapter 2.3 Heat, Temperature and Global Warming offer valuable context and analysis.

## WBBSE Class 10 Geography Chapter 2.3 Question Answer – Heat, Temperature and Global Warming

Answer in short : 2 Marks

Question 1.
What is ‘insolation’?
According to H.C. Gitchfield, radiant energy from the sun that strikes the earth is called insolation. Insolation is received in the form of shortwaves. The amount of insolation that comes to the earth’s surface is only one part of two hundred crore parts of the sun’s heat.

Question 2.
What is albedo?
A very little fraction of the sun’s energy comes to the earth as insolation, of which the total energy is not absorbed by the earth. 34% of the insolation is reflected back to space by the dust, ice crystals and cloud present in the atmosphere. This is called ‘albedo’.

Question 3.
What is heat budget?
The incoming solar radiation is balanced by an equal amount of outgoing radiation returned from the earth. This balance maintained between the insolation and outgoing radiation is called the ‘heat budget of the earth.’

Question 4.
How is the heat balance of the earth maintained ?
The average temperature of the earth remains same more or less throughout the year. The 66% of insolation received during day time is radiated back during the night. Thus, although there may be some seasonal variations, total balance of heat throughout the year is never disturbed. This is how the heat balance of the earth is maintained.

Question 5.
What is the ‘normal lapse rate of temperature’?
In the troposphere, the temperature of the atmosphere is inversely proportional to the altitude of a place. With every 1 km or 1000 m rise in altitude, temperature reduces by 6.4°C. This is known as the ‘normal lapse rate of temperature’.

Question 6.
On what factors does the amount of insolation depend?
The insolation depends on several factors like – (a) length of day (b) distance between the sun and the earth (c) clarity of the atmosphere (d) angle of incidence of solar rays etc.

Question 7.
What do you mean by ‘inversion of temperature’?
By the normal lapse rate, temperature reduces by 6.4°C with every 1 km rise in altitude. But in some cases, it is seen that temperature increases with increase in height. This phenomenon is known as the inversion of temperature. This is common in valleys of mountainous regions during early morning and late nights.

Question 8.
What do you mean by the ‘diurnal range of temperature’ ?
The range of temperature between the maximum and minimum temperatures recorded in a single day is called the diurnal range of temperature.

Question 9.
What do you mean by Average or Mean temperature ?
The average between the highest and lowest temperatures recorded in a day is called the average or mean temperature.

Question 10.
What is ‘Mean monthly temperature’ ?
The average of the mean temperatures of all the days of a month is known as the mean monthly temperature.

Question 11.
What do you mean by the annual range of temperature?
Annual range of temperature is the difference between the mean temperatures of the hottest and coldest months of the year.

Question 12.
What is average annual temperature?
The average of the mean temperatures of all the months of the year is known as the average annual temperature.

Question 13.
What do you mean by Katabatic winds?

Cold air in steep and deep valleys descends down and accumulates at the bottom due to gravity during the night. Such winds by which the cold air is forced to lie below the warm air is called Katabatic winds.

Question 14.
What do you mean by Anabatic winds?

Cold air descends into valley bottoms during the night due to Katabatic winds. During day time, this air is gradually heated and warmed. This warm air starts rising along the valley walls. This is known as Anabatic winds.

Question 15.
Name the different temperature zones of the world.
The different temperature zones of the world are :

1. The Torrid zone.
2. The North Temperature zone.
3. The South Temperate zone.
4. The North Frigid zone.
5. The South Frigid zone.

Question 16.
What do you mean by temperature zones or belts ?

Temperature of the earth’s atmosphere tends to change significantly along with change in latitudes from the equator towards the poles. The earth being round, these latitudinal zones having similar temperature conditions can be demarcated as spherical belts or zones. These are known as temperature zones.

Question 17.
What is a isotherm ?
Isotherms are imaginary lines drawn on a map joining places of the same average temperature for a specified period, supposing the places to be reduced to the sea level.

Question 18.
What is global warming ?
Global warming is the process of gradual increase of the general temperature of the earth due to increase in the use of green house gases and many other reasons. Temperature of the earth has increased by 1° from 1900 to 2000 .

Question 19.
Name some green house gases.
Some green house gases are : Carbon dioxide (C2), Carbon monoxide (CO), Methane (CH4), Nitrous Oxide (N2O), Chloro fluoro carbon (CFC), Water vapour (H2O), Ozone (O3) etc.

Question 20.
What is El Nino?
El Nino refers to the large scale ocean-atmospheric climatic interaction linked to a periodic warming in sea surface temperatures across the central and eastcentral equatorial Pacific Ocean. The effects of El Nino disturbs the global distribution of rainfall and temperature and also affect the seasons.

Question 21.
What is Solar constant?
The rate at which energy reaches the earth’s surface from the Sun through perpendicular rays, usually taken to be 1388 watts per sq. meter is called solar constant.

Question 22.
What is the heat equator?
Heat equator or thermal equator is a imagenary belt encircling the earth connects all places having highest mean annual temparature at each longitude around the globe. This line roughly followed the 5° North latitude.

Question 23.
What is Six’s maximum and minimum thermometer?
It is a instrument measuring the temperature of the day in terms of maximum and minimum value. So that it helps to calculate the average temparature and the diurnal range of temperature.

Question 24.
The earth receives one part of two hundred crore parts of sun’s radiation. Of this, about 34% of the heat energy is reflected back to space as Albedo. The remaining 66% of the heat energy that heats up the earth’s surface directly or indirectly is called Effective Solar Radiation.

Question 25.
Why does the atmosphere get heated maximum at 2 pm. even though the vertical solar rays reach the earth’s surface at 12 noon?
Answer: The most important process of heating the atmosphere is radiation by the earth’s surface. Although the earth receives maximum heat through the vertical rays of the sun at around 12 noon, the rate of radiation is maximum at 2 p.m. Hence, the atmosphere gets heated to its maximum during this time.

Question 26.
Name the hottest and coldest places of the earth.
The hottest place of the earth is Al Azizia of Libya in Africa (58°C). The coldest place is Vostok of Antarctica (-88°C).

Question 27.
When does a place experience the highest and lowest temperatures in a day?
In a day, the highest temperature is experienced around 2 p.m. and the lowest temperature is experienced just before sunrise.

Question 28.
What do you mean by Torrid Zone?
The zone spreading from $$23^{1 / 2}$$°N (Tropic of Cancer) to $$23^{1 / 2}$$° S (Tropic of Capricorn is known as the Torrid Zone. It is the hottest zone of the world.

Question 29.
What do you mean by the Temperate Zone?
The zone lying between the Tropic of Cancer ($$23^{1 / 2}$$° N) and Arctic Circle ($$66^{1 / 2}$$° N) in the northern hemisphere and the zone between the Tropic of Capricorn ($$23^{1 / 2}$$° O) and Antarctic Circle ($$66^{1 / 2}$$° S) in the southern hemisphere are known as the Temperate Zones.

Question 30.
What do you mean by the Frigid Zone?
The zone lying between the Arctic Circle ($$66^{1 / 2}$$° N) and the North Pole (90^{\circ N) in the northern hemisphere and the zone between the Antarctic Circle ($$66^{1 / 2}$$° S) and the South Pole (90° S) in the southem hemisphere are called Frigid zones.

Question 31.
What do you mean by Green House effect?
The increasing concentration of green house gases in the atmosphere like Carbon dioxide, Methane, Chloro fluoro carbon, water vapour, ozone etc. are increasing the general temperature of the atmosphere by absorbing and holding back more and more heat. This gradual process of increasing the atmospheric temperature in general is called global warming, which is the outcome of Green House effect.

Answer in brief : 3 Marks

Question 1.
Differentiate between heat and temperature of the atmosphere.

 Heat Temperature i. Heat is an energy. i. Temperature is the measure of the condition of heat of any object. ii. Heat leads to change of temperature. ii. Temperature is the result of heat. iii. Two objects having same temperature may have different heat contents. iii. Two objects having same heat content may have different temperatures. iv. Measured in calories or joules with the help of calorimeter. iv. Measured in degree centigrade or fahrenheit with the help of thermometers.

Question 2.
Why does temperature decrease with increase in altitude?

Atmospheric temperature decreases with increase in altitude for the following reasons :

1. Insolation first heats up the earth’s surface. This heat is radiated into the atmosphere gradually heating the layers from bottom to top.
2. The upper layers of the atmosphere are less dense and can rapidly radiate out heat and get cooled.
3. Pressure is less in the upper levels of the air, hence their heat absorbing capacity is also less.
4. The dust and other particles present in the upper layers absorb most of the heat and hence the air remains cool.

Question 3.
Why is lowest temperature recorded during dawn or early morning ?
The earth takes almost the whole night to radiate back the insolation that it receives during the day time. Hence it becomes coolest during the early morning or dawn, before the insolation of the next day starts.

Question 4.
What are the importances of temperature in the atmosphere?
The importances of temperature in the atmosphere are:

1. Temperature helps in birth, growth and other activities of living things on the earth.
2. It helps in germination of seeds.
3. Difference in temperature in different regions of the earth brings about growth of different species of plants and animals in different regions of the world.
4. Rate of evaporation, formation of clouds, rainfall, snowfall etc. depend on temperature conditions of a place.
5. Difference in temperature of different places leads to difference in air pressure, hence leads to generation of winds.

Question 5.
Why is annual range of temperature of deserts very high?
The reasons for great difference of temperature between hottest and coldest months in deserts are as follows :
(i) Deserts are composed of sand particles containing quartz which absorb and release heat very quickly. Hence extremes of temperature are seen.
(ii) Lack of vegetation in deserts attract very less rainfall. Hence extreme temperatures are seen.
(iii) The sandy soil of deserts have very less water holding capacity. Hence the soil gets heated very quickly and also release heat very quickly.

Question 6.
Explain the process of radiation in heating the earth’s atmosphere.
The insolation received by the earth comes in the form of short wave radiations and reach the earth’s surface without heating the atmosphere much. When this heat is radiated back by the earth in the form of long waves, it is easily absorbed by the air surrounding it. This terrestrial radiation helps to heat up the atmosphere to the maximum.

Question 7.
What is the role of conduction in heating the atmosphere ?
Conduction is the process in which one particle transmits heat to another particle. Air is a poor conductor of heat and only the lower layers of the atmosphere are heated by conduction. Thus, it is a less significant process of heating the atmosphere.

Question 8.
What is Convection?
Transfer of heat by the movement of a mass or substance from one place to another is called convection. The air particles being heated from their contact with the earth’s surface become lighter and rise. The comparatively cool air particles in the upper layers are heavier and come down slowly. This process form air currents that are known as convection currents.

Question 9.
Advection is the process by which the hot air moves along the earth’s surface horizontally and heats up the cool air of some other place. By this process, the heat of the lower latitudes is transmitted towards the higher latitudes. This process may affect temperatures of adjacent local areas as well. Eg. – ‘Loo’ is transmitted by the process of advection.

Question 10.
What are the effects of El Nino?
The effects of El Nino are :

1. Occurrence of El Nino considerably reduces rainfall in the south-east Asian countries, Indonesia, Australia and regions near the Indian ocean.
2. Rainfall occurs in Peru and Atacama desert region of South America.
3. Warm ocean curents influenced by the El Nino warm up the waters near the coastal region of Peru. Thus planktons cannot survive. This harms fish accumulation and fish catch.
4. It obstructs the blowing of monsoon winds, thus reducing rainfall.
5. It causes the weather of the western hemisphere to become warmer than normal.
6. The corals and other sea creatures may get killed.

Question 11.
What are the effects of La Nina ?
The effects of La Nina are :

1. La Nina causes heavy rainfall in western part of Pacific ocean, south and eastern Asia and north and eastern Australia.
2. In the southern hemisphere, the months from December to February remain much moist and the equatorial region in Africa remains comparatively drier.
3. Tropical cyclones increase in South and Eastern Asia.
4. Severe droughts persist in Peru and adjacent areas in South America.
5. North-western parts of North America receive more rainfall than normal.
6.  Canada experiences severe cold winters.

Question 12.
Why is lowest temperature experienced during very early morning or just before dawn?
The earth receives insolation throughout the day and radiates it back after sunset. It takes almost the whole night to radiate back all the heat before it starts receiving heat once again the next day. Hence, the atmosphere remains coolest during the dawn and very early morning, and the lowest temperatures are recorded during this time.

Question 13.
What are isotherms ? What are its characteristics?
Isotherms are imaginary lines drawn on weather maps to join places having the same temperature at the same time. The characteristics of isotherms are:

1. The isotherms run almost parallel to the latitudes.
2. They run almost straight and parallel over the oceans, but there may be deviations and ups and downs when they run over the landmasses due to variations in climatic conditions over land.
3. Value of the isotherm goes on reducing from the equatorial to polar regions.
4. Lack of cloud cover allows insolation and radiation unhindered.

Question 14.
Why are cloudless nights cooler than the cloudy nights ?
Cloud directly absorb 48% of sunlight in daytime which affect the insolation of the earth. Similarly when temperature of the earth is radiate in night time to balance the temperature on the surface of the earth, cloud prevents to radiate temperature. So that when the nights have cloud covered sky, these are warmer than the nights have clear sky or cloudless sky.

Question 15.
What do you mean by inversion of temperature?
Generally temperature decreases with increasing height of the surface at a rate of 6.4°C per 1000 m. But in some exceptional cases, temperature is increase with increasing height of the surface. This phenomena is called inversion of temperature. In mountaineous regions, at night, there has been blown cold Katabetic wind from hill top to valley. As a result temperature on the hill top area are warmer than valley region.

Question 16.
Why the places of lower altitudes are warmer than the higher altitudes?
Air density decreases with increasing height. In addition to this, amount of water vapour and dust particles are also decrease in higher altitudes. For these reasons, air is more warmer in low lying area and cooler in high.

Answer in details : 5 Marks

Question 1.
Explain the causes of difference in temperature in the atmosphere.
The factors that cause difference in temperature in the atmosphere are :
(i) Latitude : The latitudes exercise the most dominant control over the duration of sunshine and thereby the length of the day. The higher is the latitude, the lower is the amount of heat received.

(ii) Altitude : By the normal lapse rate, temperature decreases by 6.4°C with every 1 km rise in altitude. Hence, higher altitude places are colder than lower regions.
(iii) Distribution of land and water bodies : Heat absorbing capacities of land and water bodies are not equal. Latent heat capacity of water is more compared to land. Hence, extremes of temperature are noticed on land, while water bodies show moderate range of temperature.
(iv) Wind : Hot winds blowing over cold areas tend to increase atmospheric temperature and vice versa.
(v) Ocean currents : Planetary winds influence ocean currents. Warm currents may be directed towards cold regions, thus increasing the temperature of the coastal regions, and vice versa.
(vi) Slope of land : In mountainous regions, one side receives more sunlight than the other. Hence, the slope that receives more sunlight is warmer than the opposite slope which is comparatively cooler.

(vii) Cloud cover : Cloud cover acts like an umbrella preventing escape of heat from the atmosphere, thus increasing temperature. Clear sky allows insolation and radiation at greater rates, thus resulting in large temperature differences between day and night.

(viii) Rainfall : Rainfall helps to reduce heat. Hence, heavy rainfall areas near the equator may appear to be less warm compared to less rainfall areas of tropical regions.
(ix) Vegetation : Dense vegetative cover stops solar energy to heat up the ground and also attract rainfall, hence influences the temperature conditions.
(x) Soil : Soils that can hold water, control temperature conditions as they do not get heated very fast. Dry and coarse soils get heated and cooled very fast.
(xi) Industrial and urban growth : Increase in number of industries, cars, cities and several urban activities tend to heat up the atmosphere more than rural areas.

Question 2.
Describe the temperature belts/zones of the earth in brief.

The earth is divided into several temperature belts or zones according to the latitudes. They are : Torrid zone, North and South Temperate zones and North and South Frigid zone.

(i) Torrid zone: This lies from the Equator (0°) to the Tropic of Cancer ($$23^{1 / 2}$$° N) in the north and Tropic of Capricorn ($$23^{1 / 2}$$° S) in the south. The characteristics are:
(a) The sun gives vertical rays to this region.
(b) Length of day and night remains almost equal throughout the year.
(c) Average temperature is quite high (about 27°C )

(ii) North and South Temperate Zones : These zones spread from the Tropic of Cancer ($$23^{1 / 2}$$° N) to the Arctic Circle ($$66^{1 / 2}$$° N) in the north and from Tropic of Capricorn ($$23^{1 / 2}$$° S) to the Antarctic circle ($$66^{1 / 2}$$° S) in the south. The characteristics are :
(a) Sun gives medium inclined rays to this region.
(b) Average temperature is cooler than the Torrid zone.
(c) The $$23^{1 / 2}$$°-50° region is known as the warm temperate zone while the 50°-$$66^{1 / 2}$$° zone is known as the cool temperate zone.

(iii) North and South Frigid Zones : These zones spread from the Arctic Circle ($$66^{1 / 2}$$ ° N) to the North Pole (90° N) in the north and from the Antarctic Circle .($$66^{1 / 2}$$° S) to the South Pole (90° S) in the south. The characteristics are :
(a) The sun gives highly inclined rays to this region.
(b) Length of day and night is highly inequal.
(c) Average temperature remains below 0°C.
(d) Most of the time the region experiences snowfall and remains snow-covered.

Question 3.
What are the effects of global warming ?
The effects of global warming are discussed below :
i. Melting of glaciers : Global warming increases the average temperature of the earth’s atmosphere, which results in melting of ice caps and glaciers. This will submerge coastal areas due to increase in level of sea water. The fluvial cycles will be disturbed and landforms will change. Many flora and fauna may be destroyed.

ii. Climatic change : The northern hemisphere will become hotter than the southern hemisphere due to presence of more land masses here. Amount of rainfall in Tropical regions will increase by 10-15%. The northern countries may experience flood and the southern countries will experience drought in the northern hemisphere.
Summers will be longer. Chances of thunder storms and cyclones will increase.

iii. Ecosystem : Change in climate due to global warming may result in extinction of many species of birds, animals and plants.

iv. Effect on vegetation and agriculture : Excessive heat may hamper the growth of coniferous trees in hilly areas. Mangroves may be drowned due to rise in sea water level. Some crops like corn, sugarcane, jowar, bajra etc. will have increased production while crops like rice, wheat, barley, soyabean, tobacco, jute etc. will reduce their growth.

v. Spread of diseases: The germs and bacteria will become highly active and spread diseases like dengue, malaria, yellow fever, encephalitis etc. Some tropical diseases may spread to higher latitudes also.

vi. Spread of deserts : High temperature and high rates of evaporation will turn many places arid and hence boost the spread of deserts.

vii. Forest fires : Too much heat will dry up leaves and branches and cause frequent forest fires.

Question 4.
What do you mean by green house gases? What are the uses of green house gases?
The gases which play an important role in increasing the average temperature of the earth’s atmosphere are called Green House Gases. Some of the Green House Gases are Carbon Dioxide (CO2), Carbon Monoxide (CO), Methane (CH4), Chloro fluoro carbon (CFC), Nitrous Oxide (N2O), Water vapour, etc. Uses – The Green House Gases are prepared naturally in the environment and are also sometimes the outcome of human activities. These gases are very important for life activities. The sun’s energy reaches the earth’s surface daily as insolation, and is radiated back daily. The Green House Gases trap the outgoing infrared radiation and send it back towards the earth’s surface. This helps to keep the earth’s atmosphere warm, which would have otherwise become so chilled due to out-radiation that no life would have been possible on earth. But the problem is, if the amount of Green House Gases increases drastically, they will hold back so much heat that it will increase the atmospheric temperature at alarming rates. This condition will also be not suitable for existence of life on earth.

## WBBSE Class 10 Geography Solutions Chapter 2.2 Layers of the Atmosphere

Detailed explanations in West Bengal Board Class 10 Geography Book Solutions Chapter 2.2 Layers of the Atmosphere offer valuable context and analysis.

## WBBSE Class 10 Geography Chapter 2.2 Question Answer – Layers of the Atmosphere

Answer in short : 2 Marks

Question 1.
Name the different layers of the atmosphere.
The different layers of the atmosphere are – Troposphere, Stratosphere, Mesosphere, Ionosphere or Thermosphere and Exosphere.

Question 2.
What is the Tropopause?
Tropopause is the transition zone between the troposphere and the stratosphere. It extends for about 2-3 km. Here the temperature remains constant.

Question 3.
What is the Stratopause?
Stratopause is the transition zone between the stratosphere and the mesosphere. Temperature in this zone remains constant.

Question 4.
What is the mesopause ?
Mesopause is the transition zone between the mesosphere and the ionosphere or the thermosphere. Temperature in this zone remains constant.

Question 5.
What is the ozone layer ?
There is a layer in the stratosphere at a height of 20-45 km, which has a high concentration of ozone gas. This portion of the stratosphere is called the ozone layer or the ozonosphere.

Question 6.
Describe the exosphere.
The exosphere lies above the thermosphere and extends up to 960 km. It gradually merges with the interplanetary space.

Question 7.
What is normal lapse rate?
A lapse rate is the rate at which temperature of the atmosphere decreases as the altitude increases in troposphere. Temperature decrease at the rate of 6.4°C per 1000 mt. in the troposphere.

Question 8.
What is the Van Allen radiation belt ?
Energetic charged particles mostly originated from solar wind are captured by and held around the planet earth called Van Allen radiation belt. Earth has two such belts.

Question 9.
What do you mean by nacreaous cloud ?
One of the polar stratospheric clouds, that consist of only ice crystals are called nacreous cloud. These are not harmful. These are mostly observed during twillight. These are not precipitation cloud.

Answer in briefly : 3 Marks

Question 1.
Describe the Troposphere.
The lower-most layer of the atmosphere lying closest to the earth’s surface is called the Troposphere. It extends up to 18 km at the equator and 8 km at the poles. Temperature decreases by 6.4°C with rise of every 1000 m or 1 km. This is called the lapse rate of temperature. Most of the weather phenomena occur in this zone. Eg. – clouds, rainfall, storms etc.

Question 2.
Describe the stratosphere.
The second layer of the atmosphere that lies above the troposphere and extends up to 80 km above the earth’s surface is called the stratosphere. In this zone, temperature goes on increasing with increase in height (about 4°C for every 50 km). A significant concentration of ozone gas is found in this layer, known as the Ozonosphere. Stratosphere has very less atmospheric disturbances. Some cirrus clouds form in the lower levels of this layer.

Question 3.
Describe the mesosphere.
The third layer of the atmosphere that lies above the stratosphere is known as the mesosphere. This zone is marked by decrease in temperature with height. This is the coldest layer of the atmosphere. Meteors that come from the outer space towards the earth get burnt within this layer.

Question 4.
What are the characteristics of the ozone layer?
The ozone layer is a part of the stratosphere. The main characteristics of this layer are :

1. Ozone constitutes about 1% of the stratospheric air.
2. Ozone is produced by the action of solar radiation on ordinary oxygen atoms.
3. Ozone layer acts as a shield, protecting us by absorbing most of the harmful ultra-violet rays of the sun.
4. Density of ozone gas is expressed by the ‘Dobson’ unit (DU). Lowest density of the layer is found in the equatorial region.

Question 5.
What do you mean by ozone depletion and ozone hole.
Depletion or breaking of ozone molecules in the atmosphere is known as ozone depletion.

1. Average natural concentration of ozone dropped by 50% in 1987.
2. In some areas, the ozone layer totally disappeared which resulted in formation of ozone-less patches. These hollows are called ozone holes.
3. The chloro fluoro carbons (CFCs) are the chief culprits causing ozone depletion.

Question 6.
Mention the characteristics of the lonosphere.
The layer of the atmosphere lying above the mesosphere is called the ionosphere or thermosphere. The characteristics of this layer are :

1. This layer extends up to 500 km above the mesopause.
2. The gases absorb X-rays and Ultra-violet rays and the temperature increases.
3. Radio waves are reflected back from this layer, thus helping in radio communication.
4. Auroras or strange interesting lights are produced in the ionosphere. These are called Aurora Borealis in the northem hemisphere and Aurora Australis in the southern hemisphere.

Question 1.
Discuss the layers of the atmosphere.
[Write about all the layers of the atmosphere discussed previously.]

## WBBSE Class 10 Geography Solutions Chapter 2.1 Concepts of Atmosphere

Detailed explanations in West Bengal Board Class 10 Geography Book Solutions Chapter 2.1 Concepts of Atmosphere offer valuable context and analysis.

## WBBSE Class 10 Geography Chapter 2.1 Question Answer – Concepts of Atmosphere

Answer in short : 2 Marks

Question 1.
What is atmosphere?
The thick blanket of air surrounding the earth, extending to a height of about 10,000 km above its surface, is known as the atmosphere. It is hold in place by the gravitational force of the earth.

Question 2.
What are Aerosols?
Aerosols are very fine solid particles that remain suspended in the air. They act as the base of condensation for rainfall, snowfall, fog, dew, mist etc. They absorb solar radiation and keep the atmosphere warm. They are responsible for reflection of sunlight causing dawn and twilight. They also reflect light and make the sky appear blue.

Question 3.
Name the major gases of the atmosphere.
The main gases of the atmosphere are : Nitrogen (78.084%), Oxygen (20.946%), Argon (0.934 %), Carbon dioxide (0.033 %).
Other gases present are : Neon, Helium, Krypton, Xenon, Hydrogen, Methane, Nitrous oxide, Radon, Ozone etc. Amongst these, Nitrogen, Argon, Neon, Helium, Krypton and Xenon are known as noble or inert gases.

Question 4.
What are the importances of oxygen in the atmosphere?
Oxygen occupies about 21 % of the atmosphere. Importances of this gas are:

1. Oxygen helps to support life.
2. It helps to provide heat and energy in living organisms.
3. It helps in burning of fire.
4. It helps in the process of oxidation.
5. It causes rusting of iron.

Question 5.
Mention the importances of nitrogen gas in the atmosphere.
Nitrogen occupies about 78 % of the atmosphere. Its importances are :

• Protein synthesis in living organisms.
• Increasing soil fertility.
• Manufacturing fertilisers.

Question 6.
Mention the importances of carbon dioxide.
Carbon dioxide occupies a negligible percentage (0-033 %) in the atmosphere, but it is a very important gas.

1. It helps in photosynthesis and formation of glucose in plants.
2. It helps in carbonation of rocks during weathering.
3. It controls atmospheric temperature.
4. It controls or influences the climate.
5. It helps in weathering of limestone.

Question 7.
What is the homosphere ?
According to D. S. Lal, “the term homosphere means the zone of homogenous composition’. It refers to that part of the atmosphere, where the composition is uniform.

Question 8.
What is the heterosphere?
The atmosphere above the homosphere up to a height of 10,000 km is not uniform in composition with reference to its chemical composition and proportion. This part of the atmosphere is known as the heterosphere.

Question 9.
Why are the inert gases called so ?
Gases like Nitrogen, Argon, Neon, Helium, Krypton and Xenon do not react with the components of atmosphere and the earth’s surface under normal circumstances. Hence they are called ‘inert gases’.

Question 10.
What is density of the atmosphere?
The amount of gas molecules or the mass of gas molecules present in a unit volume of the atmosphere is known as the density of the atmosphere.

Answer in briefly : 3 Marks

Question 1.
What are the importances of water vapour in the atmosphere?

1. Water vapour not only absorbs the sun’s incoming radiation (insolation), but also absorbs the heat radiated back by the earth, thus keeping the atmosphere warm.
2. It helps in formation of clouds, fog, dew, rainfall, snowfall etc.
3. Amount of water vapour influences occurrence of rainfall, snowfall, storms, and other environmental activities.
4. It helps the hydrological cycle to function properly.

Question 2.
Describe the importances of dust particles in the atmosphere.
Dust particles mix with the atmosphere from various sources like – soil particles, salt particles from seas, solid particles coming out of cars and chimney smoke, cinder, ash etc. from volcanoes, ash from forest fires etc.
Importances of these particles in the atmosphere are :

• The dust particles act as the base of condensation for the formation of clouds, fog, mist, dew, rainfall, snowfall etc.
• They reflect and refract light.
• They help in occurrence of dawn, twilight and help the sky appear blue.
• They absorb insolation and back radiation from the earth and help to keep the atmosphere warm.

Question 3.
Mention the characteristics of the atmosphere.
The main characteristics of the atmosphere are :

1. The atmosphere extends up to 10,000 km above the surface of the earth.
2. Density of the atmosphere reduces with height.
3. This contains the most important components that are inevitable for plant and animal life.
4. The atmosphere is invisible, but its presence can be felt evidently.

Question 4.
What are the characteristics of the ozone layer?
Ozone gas is concentrated in the stratosphere at an altitude of 25-50 km above the earth’s surface. This layer is also called the ozonosphere. The characteristics are :

• 90% of ozone gas lies in this layer.
• It filters the ultra-violet rays that comes from the sun.
• It protects the biotic world from damage and disaster.
• Density of ozone gas is expressed in Doloson Unit (DU).
• Density of ozone gas is 250 DU near the equator, 350 DU in the mid latitudes and 450 DU in the polar regions.

Answer in details : 5 Marks

Question 1.
Name the main components of the atmosphere and discuss about them.
The components of the atmosphere can be classified into two parts :
(a) Permanent components : The permanent components mainly constitute the gaseous elements those proportion does not change in the atmosphere.
They are : Nitrogen (78.084%), Oxygen (20.946%), Argon (0.934%), Carbon dioxide (0.033 %) and other gases like Nitrogen, Neon, Helium, Hydrogen, Xenon, Krypton, Methane, Radon, Ozone etc.

(b) Variable components : These include :
i) Water vapour : Amount of water vapour varies from place to place, time to time and depends on factors like heat, presence of water bodies, wind speed, humidity etc.

ii) Dust particles : Tiny solid particles coming from dust, salt grains, pollen grains, smoke, soot etc. remain suspended in the air in different amounts in different places. These are also called aerosols.

iii) Carbon dioxide : CO2 is an important variable gas. Currently it constitutes about 0.03 %. of the atmosphere. It is a potent green house gas and plays a vital role in controlling the earth’s surface temperature.

Question 2.
Classify the layers of the atmosphere according to temperature.
The atmosphere has been classified into five layers by Pattersen according to temperature.
i) Troposphere : The troposphere extends up to 18 km in the equatorial region to 7-8 km in the polar region above the earth’s surface. Temperature of this layer reduces by 6.4°C for every 1000 ~m rise in altitude. The lowest temperature

recorded here is -80°c at the highest limits of the troposphere near the equator.

ii) Stratosphere: This layer is above the troposphere, and is separated by the tropopause. Temperature of this layer goes on increasing with rise in altitude. It spreads up to 50 km above the earth’s surface. Temperature reaches to 0°C at the highest levels of the stratosphere. This layer is void of clouds and rainfall. A concentrated layer of ozone gas is found within this layer.

iii) Mesosphere : After the stratosphere, the mesosphere lies up to 80 km above the earth’s surface. This is the last limit of the homosphere. Temperature decreases with increase in altitude. This layer lies between the stratopause and the mesopause.

iv) Ionosphere or Thermosphere : This layer spreads up to 500 km from the earth’s surface after the mesopause. Temperature increases rapidly in this layer with rise in altitude, and reaches about 1200°C at the upper limits. In this layer, constant interaction of ultra violet rays, x-rays, α-rays, β-rays and γ-rays cause ionisation of the gases.

v) Exosphere : This layer spreads from 500-750 km above the earth’s surface.

Question 3.
Differentiate between the Homosphere and the Heterosphere.

 Homosphere Heterosphere i. The ratio of component gases of the atmosphere remains more or less same up to 88 km altitude. This layer is called the homosphere. i. The ratio of component gases of the atmosphere does not remain the same beyond 88 km altitude. This layer is called the heterosphere. ii. It spreads from 0-88 km above the earth’s surface. ii. It spreads from 88-10,000 km above the earth’s surface. iii. It comprises the troposphere, stratosphere, mesosphere and parts of the thermosphere. iii. It comprises parts of thermosphere, the exosphere and magnetosphere. iv. It consists of gases, water vapour and dust particles. iv. It consists of very little traces of water vapour and dust particles. The gases mostly lie in ionised forms. v. All the weather conditions and changes occur within 6 km of the homosphere. v. No weather changes are noticed in the heterosphere. vi. Lower layers of the homosphere support life and related activities. The ozone layer protects the earth from sun’s harmful ultraviolet rays. vi. The ionised gases of the heterosphere help in transmission of radio waves, thus helping to run mobiles, wireless sets, radios and other devices.

Multiple Choice Questions (MCQ) : 1 Mark

Question 1.
The tropopause occurs at the equator at a height of :
(A) 5 km.
(B) 20 km.
(C) 18 km.
(D) 25 km.
(C) 18 km.

Question 2.
97 % of the atmosphere lies within _____ km. of the surface of the earth :
(A) 50 km.
(B) 29 km.
(C) 5 km.
(D) 15 km.
(B) 29 km.

Question 3.
The lower layer lonosphere is known as :
(A) Troposphere
(B) Stratosphere
(C) Ozonosphere
(D) Thermosphere
(D) Thermosphere

Question 4.
The Mediterranean region receives rainfall :
(A) From trade winds in summer
(B) From trade winds in winter
(C) From westerlies in winter
(D) By convection in summer
(C) From westerlies in winter

Question 5.
The atmospheric layer which reflects radio waves is called :
(A) Exosphere
(B) Stratosphere
(C)Troposphere
(D)Thermosphere
(C)Troposphere

Question 6.
Atmosphere gets heated up :
(A) In the early morning
(B) At mid day
(C) At 2:00 pm.
(D) In the late evening
(C) At 2:00 pm.

Question 7.
The most important component of the atmosphere which causes many weather phenomena is :
(A) Oxygen
(B) Carbon dioxide
(C) Nitrogen
(D) Water vapour
(D) Water vapour

Question 8.
The lower layer of the atmosphere is known as :
(A) Mesosphere
(B) Stratosphere
(C) Ionosphere
(D) Troposphere
(D) Troposphere

Question 9.
Tropopause is the zone that separates :
(A) Earth’s surface and Troposphere
(B) Troposphere and Stratosphere
(C) Stratosphere and lonosphere
(D) Earth’s surface and lonosphere
(B) Troposphere and Stratosphere

Question 10.
Ionosphere is :
(A) The lowest region of the atmosphere
(B) The highest region of the atmosphere
(C) The middle most region of the atmosphere extending from 40 km. to 75 km.
(D) None of the above
(B) The highest region of the atmosphere

Question 11.
The tropopause is situated at a height of over the equator
(A) 10 km.
(B) 15 km.
(C) 18 km.
(D) 22 km.
(C) 18 km.

Question 12.
Most of the weather phenomena take place in the :
(A) Stratosphere
(B) Ionosphere
(C) Troposphere
(D) Mesosphere
(C) Troposphere

Question 13.
________ of the effective atmosphere is found up to the height of 29 km.:
(A) 29 %
(B) 35 %
(C) 90 %
(D) 97 %
(D) 97 %

Question 14.
Percentage of argon in the atmosphere is :
(A) 1 %
(B) 1.5 %
(C) 0.30 %
(D) 0.93 %
(D) 0.93 %

Question 15.
Which one of the following is lowermost layer?
(A) Stratosphere
(B) Troposphere
(C) Troposphere or Stratosphere
(D) It is not certain
(B) Troposphere

Question 16.
Normal Lapse rate is supposed to be:
(A) 6.5°C per 100m
(B) 6.5°C per 10m
(C) 6.5°K per 100m
(D) 6.0°K per 100m
(A) 6.5°C per 100m

Question 17.
The average height of the troposphere over the poles is around :
(A) 16 km
(B) 14 km
(C) 8 km
(D) 6 km
(D) 6 km

Question 18.
Medium and high frequency radio waves are reflected by which layer?
(A) E layer
(B) G layer
(C) F layer
(D) All of these
(C) F layer

Question 19.
Isobars are :
(A) The lines of equal atmospheric pressure
(B) The lines of unequal atmospheric pressure
(C) The parallel lines of atmospheric pressure
(D) None of the above
(A) The lines of equal atmospheric pressure

Question 20.
What is the characteristic of planetary winds:
(A) These flow from the belts of high pressure to the belts of low pressure
(B) These flow from the belts of low pressure to the belt of high pressure
(C) These do not flow to any centre of pressure
(D) None of these
(A) These flow from the belts of high pressure to the belts of low pressure

Question 21.
Wind in the southern hemisphere deflects towards left :
(A) Due to rotation of the earth
(B) Due to temperature
(C) Due to heating
(D) None of these
(A) Due to rotation of the earth

Question 22.
The instrument used for measuring the atmospheric pressure is called:
(A) Barometer
(B) Hygrometer
(C)Altimeter
(D) Thermometer
(A) Barometer

Question 23.
The mountaineers climbing the high peaks carry:
(A) Helium
(B) Nitrogen
(C) Hydrogen
(D) Oxygen
(D) Oxygen

Question 24.
The sub-tropical high pressure belts are also known as :
(A) Doldrums
(B) Roaring forties
(C) Torrid zone
(D) Horse latitudes
(B) Roaring forties

Question 25.
Besides the local winds and permanent winds, another type of winds are :
(A) Prevailing winds
(B) Horizontal winds
(C) Vertical winds
(D) Periodic winds
(D) Periodic winds

Question 26.
If the incoming solar radiation is 100 % then scattering by dust particles is :
(A) 27 %
(B) 2 %
(C) 6 %
(D) None of these
(C) 6 %

Question 27.
The amount of heat needed to raise the temperature of one gram of substance by 1°C is called :
(A) Specific heat
(B) Relative heat
(C) Absolute heat
(D) None of these
(A) Specific heat

Question 28.
Horse latitudes are found between the latitudes :
(A) 5°N to 5°S
(B) 25°-35° in both the hemisphere
(C) 30°-45° in both the hemisphere
(D) None of these
(B) 25°-35° in both the hemisphere

Question 29.
The zone of _____ wind is also known as Hadley cells.
(A) Westerly
(B) Easterly
(D) None of these

Question 30.
Which type of rainfall is called relief rainfall ?
(A) Convectional
(B) Orographic
(C) Cyclonic
(D) All of these
(B) Orographic

Question 31.
Which of the following instruments is used for measuring the temperature?
(A) Barometer
(B) Thermometer
(C) Hydrometer
(D) Hygrometer
(B) Thermometer

Question 32.
Anemometer is used to measure :
(A) The velocity of the earth
(B) The velocity of the waves
(C) The velocity of the winds
(D) The velocity of earthquake waves
(C) The velocity of the winds

Question 33.
The actual mass of water vapour per unit volume of air is known :
(A) Relative humidity
(B) Absolute humidity
(C) Specific humidity
(D) Degree of saturation
(B) Absolute humidity

Question 34.
The prevailing north-western westerly winds which blow vigorously between 40° and 60° south latitudes throughout the year are known:
(A) Sirocco
(B) Roaring forties
(C) Harmattan
(D) Pampero
(B) Roaring forties

Question 35.
About 34 per cent of insolation being returned to space as short waves are known as :
(B) The earth’s Albedo
(C) Heat Transfer
(D) Terrestrial heat balance
(B) The earth’s Albedo

Question 36.
The boundary zone developed at or near the mass of warm air where an advancing cold air strikes and forces the warm air upward is called :
(A) Warm front
(B) Cold front
(C) Occuluded front
(D) Warm air mass
(B) Cold front

Question 37.
The rate of temperature decreases (C°) in the atmosphere per 1000 metre ascent is :
(A) 3.6° C
(B) 6.4° C
(C) 7.4° C
(D) 8.6° C
(B) 6.4° C

Question 38.
Inversion of temperature is :
(A) Increase of temperature with altitude
(B) Decrease of temperature with altitude
(C) Uniform temperature
(D) Decrease of temperature with latitudes
(A) Increase of temperature with altitude

Question 39.
The albedo of earth is :
(A) 25 %
(B) 35 %
(C) 45 %
(D) 55 %
(B) 35 %

Question 40.
The total annual insolation is greatest at –
(A) The tropic of Cancer
(B) The tropic of Capricorn
(C) The equator
(D) The arctic circle
(D) The arctic circle

Question 41.
The dry adiabatic lapse rate is :
(A) 6.4°C
(B) 10°C
(C) 8.5°C
(D) 2°C
(B) 10°C

Question 42.
Jet stream is a :
(A) Warm Current
(B) Cold Current
(C) Local Wind
(D) Upper air westerlies
(D) Upper air westerlies

Question 43.
The type of rainfall common at equatorial region is :
(A) Convectional
(B) Orographic
(C) Cyclonic
(D) Relief
(A) Convectional

Question 44.
Doldrum is a zone of :
(A) Intertropical Convergence
(B) Intertropical Divergence
(C) Local wind
(D) Frontolysis
(A) Intertropical Convergence

Question 45.
The highest temperature is recorded by :
(A) Mercurial thermometer
(B) Hot thermometer
(C)Alcohol thermometer
(D) Minimum thermometer
(A) Mercurial thermometer

Question 46.
The lowest temperature is recorded by :
(A) Maximum thermometer
(B) Mercurial thermometer
(C) Alcohol thermometer
(D) None of these
(C) Alcohol thermometer

Question 47.
What is the name of the scale meant for recording weather conditions?
(A) Fahrenheit
(B) Barometer
(C) Hydrometer
(D) Opisometer
(A) Fahrenheit

Question 48.
Another scale used for recording weather conditions is known as :
(A) Hygrometer
(B) Hydrometer
(C) Opisometer

Question 49.
Which of the following components of the atmosphere has increased during the last 200 years?
(A) Oxygen
(B) Water vapour
(C) Carbon dioxide
(D) Nitrogen
(C) Carbon dioxide

Question 50.
The velocity of wind is recorded by :
(A) altimeter
(B) Barometer
(C) Anemometer
(D) Aneroid barometer
(C) Anemometer

Question 51.
Horse latitudes lie :
(A) In the vicinity of 30° latitude both north and south of the equator
(B) In the vicinity of 50° latitude both north and south of the equator
(C) Between 50° and 60° latitude both north and south of equator
(D) None of these
(A) In the vicinity of 30° latitude both north and south of the equator

Question 52.
When warm air moves into a region of cold air it leads to the formation of :
(A) Cold front
(B) Warm front
(C) Cyclone
(D) Anticyclone
(B) Warm front

Question 53.
Hurricanes are generally :
(A) Active over land
(B) Active over the sea
(C) Travelling in families
(D) Dust storms
(B) Active over the sea

Question 54.
The tropical cyclones of the Bay of Bengal are usually called :
(A) Typhoons
(B) Hurricanes
(C) Depressions
(D) Willy willy
(A) Typhoons

Question 55.
Jet Stream blows :
(A) From west to east
(B) From east to west
(C) From north to south
(D) None of these
(A) From west to east

Question 56.
In which region does rainfall occur throughout the year?
(A) Equatorial region
(B) Polar region
(C) Sub-polar region
(D) Middle-latitude region
(A) Equatorial region

Question 57.
China type (Cw) has dry winter season because :
(A) Cool dry winds blow from interior of the continent
(B) There are no clouds
(C) Temperature is low
(D) Humidity is low
(A) Cool dry winds blow from interior of the continent

Question 58.
Tropical deserts receive scanty rainfall because:
(A) They are away from the equator
(B) They do not have clouds
(C) Trade winds blow from the hot interior of the continent
(D) Cool currents blow along the coast
(C) Trade winds blow from the hot interior of the continent

Question 59.
Which of the following is not a tropical desert:
(A) Kalahari
(B) Atacama
(C) Arabia
(D) Mongolia
(D) Mongolia

Question 60.
Conduction is a process :
(A) That conducts heat from warmer to the cooler region until the two objects coming into contact get the same temperature
(B) That conducts heat from cooler to the warmer region
(C) That does not conduct heat to any of the objects coming into contact
(D) None of the above
(A) That conducts heat from warmer to the cooler region until the two objects coming into contact get the same temperature

Question 61.
Humidity is the result of :
(A) Evaporation
(B) Transpiration
(C) Presence of heat
(D) Presence of moisture content in the air
(D) Presence of moisture content in the air

Question 62.
Specific humidity is :
(A) The indicator of density of water vapour
(B) The maximum water content existing in the atmosphere
(C) It is the ratio of the mass of water vapour present to the total mass of air
(D) None of the above
(C) It is the ratio of the mass of water vapour present to the total mass of air

Question 63.
What is relative humidity ?
(A) It is the ratio of specific humidity
(B) It is the indicator of moisture content of atmosphere
(C) It is the indicator of density of water vapour
(D) None of the above
(A) It is the ratio of specific humidity

Question 64.
Annual range of temperature is maximum in :
(A) Equatorial region
(B) Sub-tropical region
(C) Middle latitudes
(D) Polar regions
(C) Middle latitudes

Question 65.
The winds blowing from subtropical high pressure to sub-polar low pressure are :
(A) Westerlies
(B) Easterlies
(C) Polar winds
(D) Jet Stream
(B) Easterlies

Question 66.
Doldrum belt is the region of :
(A) High pressure and strong winds
(B) Moderate pressure
(C) Low pressure and calm conditions
(D) None of these
(C) Low pressure and calm conditions

Question 67.
Animometer is :
(A) An instrument that measures the wind speed
(B) An instrument that measures the air masses
(C) An instrument that measures speed
(D) An instrument that measures velocity
(A) An instrument that measures the wind speed

Question 68.
(A) Moisturous
(B) Hot and wet
(C) Dry
(D) Wet
(C) Dry

Question 69.
Beaufort scale is used to measure :
(A) Air pressure
(B) Wind velocity
(C) Wind direction
(D) Humidity
(B) Wind velocity

Question 70.
The Torrid Zone lies between :
(A) The Equator and the Tropic of Cancer
(B) The Equator and the Tropic of Capricorn
(C) The Tropic of Cancer and the Tropic of Capricorn
(D) Precipitation and natural vegetation
(C) The Tropic of Cancer and the Tropic of Capricorn

Question 71.
Nitrogen and Oxygen constitute of the total gaseous composition of the atmosphere.
(A) 93 %
(B) 95 %
(C) 97 %
(D) 99 %
(D) 99 %

Question 72.
Which of the following is a Greenhouse gas ?
(A) Carbondioxide
(B) Ozone
(C) Oxygen
(D) Nitrogen
(A) Carbondioxide

Question 73.
Most of the ultraviolet rays one absorbed by
(A) Hydrogen
(B) Nitrogen
(C) Ozone
(D) Carbondioxide
(C) Ozone

Question 74.
________ is a permanent gas in the atmosphere.
(A) Carbondioxide
(B) Ozone
(C) Nitrogen
(D) Hydrogen
(C) Nitrogen

Question 75.
Atmospheric water vapour content is highest in the
(A) Temperate region
(B) Polar region
(C) Equatorial region
(D) Tropical region
(D) Tropical region

Question 76.
The English word ‘atmosphere’ comes from the green word ‘atmos’, which means-
(A) Air
(B) Vapour
(C) Evaporation
(D) Envelop of gases
(B) Vapour

Question 77.
The sky appears blue due to selective scattering of solar radiation by-
(A) Salt particles
(B) Dust particles
(C) Both A and B
(D) None of these
(B) Dust particles

Question 78.
Troposphere contains about ______ of the total gaseous mars of the atmosphere.
(A) 70 %
(B) 75 %
(C) 80 %
(D) 85 %
(B) 75 %

Question 79.
Which of the following is also called the convective region?
(A) lonosphere
(B) Ozonosphere
(C) Troposphere
(D) Mesosphere
(C) Troposphere

Question 80.
The wind velocity increases with height in the –
(A) Troposphere
(B) Stratosphere
(C) Stratopause
(D) lonosphere
(A) Troposphere

Question 81.
The thickness of the stratosphere is highest at the –
(A) Poles
(B) Tropics
(C) Equator
(D) All of these
(A) Poles

Question 82.
Which gas protects us from the harmful ultraviolet rays ?
(A) Nitrogen
(B) Oxygen
(C) Ozone
(D) Carbondioxide
(C) Ozone

Question 83.
The credit for the discovery of ionosphere goes to –
(A) Napier Shaw
(B) Picardy
(C) Kennelly and Heaviside
(D) Teisserence de Bort
(C) Kennelly and Heaviside

Question 84.
During the winter season, the stratosphere is warmest between the latitudes
(A) 50°-60°
(B) 50°-65°
(C) 50°-70°
(D) 50°-75°
(A) 50°-60°

Question 85. ‘Aurora Borealis’ is produced in the
(A) Exosphere
(B) Ionosphere
(C) Mesosphere
(D) Stratosphere
(B) Ionosphere

Question 86.
Match the following

Question 87.
helps to keep the temperature of the earth’s surface moderate.
(A) Gases
(B) Water vapour
(C) Particulate matter
(D) All of these
(B) Water vapour

Question 88.
Which of the following is an important feature of the Troposphere?
(A) It is isothermal in character
(B) There is maximum concentration of ozone
(C) There is a decrease of temperature with increase in altitude at a mean lapse rate of about 6.5°C
(D) There is a steep rise in temperature
(C) There is a decrease of temperature with increase in altitude at a mean lapse rate of about 6.5°C

Question 89.
The outermost layer of the atmosphere is known as
(A) Exosphere
(B) lonosphere
(C) Mesosphere
(D) Ozonosphere
(A) Exosphere

Question 90.
The gases which are predominant in the exosphere are
(A) Hydrogen and Neon
(B) Hydrogen and Ozone
(C) Hydrogen and Methane
(D) Hydrogen and Helium
(D) Hydrogen and Helium

Question 91.
Troposphere, Stratosphere and Mesosphere are subdivisions of the
(A) Homosphere
(B) Heterosphere
(C) Chemosphere
(D) Pyrosphere
(A) Homosphere

Question 92.
The atmosphere receives most of its energy from
(A) Sun
(C) Albedo
(A) Sun

Question 93.
The transfer of heat through the molecules of matter in any body is called
(B) Convection
(C) Conduction
(B) Convection

Question 94.
The process of transfer of energy from one body to another without the aid of any material is called –
(A) Conduction
(C) Convection
(C) Convection

Question 95.
What percentage of outgoing longwave terrestrial radiation is absorbed by atmosphere?
(A) 60 %
(B) 70 %
(C) 80 %
(D) 90 %
(D) 90 %

Question 96.
The increase in the concentration of CO2 in the atmosphere will increase the
(A) Heat
(B) Greenhouse effect
(D) Evaporation
(B) Greenhouse effect

Question 97.
The earth’s surface recelves maximum solar energy at about
(A) 11: 00 am
(B) 12 Noon
(C) 1: 00 pm
(D) 2: 00 pm
(B) 12 Noon

Question 98.
The thermal inversion in the upper air is caused by the presence of
(A) Carbondioxide
(B) Ozone layer
(C) Water vapour
(D) None of these
(B) Ozone layer

Question 99.
Which of the following surface receives very low insolation ?
(A) Snow cover
(B) Sand
(C) Black soil
(D) Forest
(A) Snow cover

Question 100.
The horizontal distribution of temperature is represented and studied with the help of –
(A) Isotherms
(B) Isobars
(C) Isohyte
(D) Isohayline
(A) Isotherms

Question 101.
The weight of air on unit area of the earth is called
(A) Air weight
(B) Air pressive
(C) Air mass
(D) Air volume
(B) Air pressive

Question 102.
The atmospheric pressure is maximum at the
(A) Coastal areas
(B) Interior parts of continents
(C) Sea level
(D) All of these
(C) Sea level

Question 103.
The standard air pressure at sea level is –
(A) 1018.25 m
(B) 1021.25 m
(C) 1013.25 m
(D) 1015.25 m
(C) 1013.25 m

Question 104.
Which of the following pressure belt is thermally inducted?
(A) Subtropical high pressure belt
(B) Equatorial low pressure belt
(C) Subpolar low pressure belt
(D) Both ‘A’ and ‘C’
(B) Equatorial low pressure belt

Question 105.
The winds blowing almost in the same direction throughout the year are called
(A) Prevailing winds
(B) Seasonal winds
(C) Local winds
(D) Variable winds
(A) Prevailing winds

Question 106.
Winds blowing in a particular locality are called
(A) Seasonal winds
(B) Local winds
(C) Mountain winds
(D) Land and sea breeze
(B) Local winds

Question 107.
Which winds are famous for there steady direction and wind speed?
(A) Westerlies
(B) Easterlies
(C) Polar winds

Question 108.
The subtropical high pressure belt is the source of –
(A) Polar winds
(C) Local winds
(D) Westerlies

Question 109.
The continent having the greatest monsoonal influence is –
(A) North America
(B) Asia
(C) South America
(D) Australia
(B) Asia

Question 110.
Which of the following wind prevails on the eastern slopes of the Rocky mountains in Wyoming and Montana?
(A) Santa Ana
(B) Mistral
(C) Sirocco
(D) Chinook
(D) Chinook

Question 111.
Which of the following is an intensely hot and dry wind of the Asiatic and African deserts?
(A) Khamsin
(B) Sirocco
(C) Simoom
(D) Harmatian
(C) Simoom

Question 112.
Which of the following is a cold north-western wind that blows towards the western mediteranean basin from higher elevations?
(A) Mistral
(B) Bora
(C) Blizzard
(D) Harmattan
(A) Mistral

Question 113.
The most important form of suspended water droplets caused by condensation is
(A) Fog
(B) Ice
(C) Cloud
(D) Frost
(C) Cloud

Question 114.
is the most common form of precipitation
(A) Snow
(B) Rainfall
(C) Sleet
(D) Hail
(B) Rainfall

Question 115.
Which of the following is a warm weather phenomena associated with lightning and thunder?
(A) Convectional rainfall
(B) Orographic rainfall
(C) Frontal rainfall
(D) All of these
(A) Convectional rainfall

Question 116.
Which of the following rainfall occur due to ascent of air, forced by mountain barrier?
(A) Convectional rainfall
(B) Orographic rainfall
(C) Cyclonic rainfall
(D) All of these
(B) Orographic rainfall

Question 117.
Indian monsoon is the best example of
(A) Convectional rainfall
(B) Cyclonic rainfall
(C) Orographic rainfall
(D) None of these
(C) Orographic rainfall

Question 118.
Southern plateau in the east of Western Ghats is the example of
(A) Inversion of rainfall
(B) Cloud instability
(C) Maximum rainfall line

Question 119.
The precipitation associated with cold fronts is always in the form of
(A) Snow
(B) Drizzle
(C) Thunder shower
(D) Sleet
(C) Thunder shower

Question 120.
Most of the rains of temperate regions are received through
(A) Cyclonic rainfall
(B) Orographic rainfall
(C) Convectional rainfall
(D) None of these
(A) Cyclonic rainfall

Question 121.
Which of the following pressure belt is called ‘Horse latitude’ ?
(A) Polar high pressure belt
(B) Subpolar low pressure belt
(C) Subtropical high pressure belt
(D) Equatorial low pressure belt
(C) Subtropical high pressure belt

Question 122.
Which of the following winds blows parallel to the isobars, generally at a height of 600 m ?
(B) geostrophic wind
(C) Invariable wind
(D) Surface wind
(B) geostrophic wind

Question 123.
The direction of surface wind is usually controlled by
(B) Rotation of the earth
(C) Deflection forces
(D) Both ‘A’ and ‘B’
(D) Both ‘A’ and ‘B’

Question 124.
The zone extending 5°N to 5°S along the equator is called
(A) Doldrums
(B) Horse latitudes
(D) Westerlies
(A) Doldrums

Question 125.
Winter precipitation in the Northern part of India is an example of ______ rainfall.
(A) Orographic
(B) Monsoonal
(C) Convectional
(D) Cyclonic
(D) Cyclonic

Question 126.
The monsoon region is located in the ______ rainfall zero.
(A) Mediterranean
(C) Subtropical
(D) Midlatitude

Question 127.
______ is an example of atmospheric disturbance.
(A) Rain
(B) Cyclone
(C) Fronts
(D) Winds
(B) Cyclone

Question 128.
Temperate cyclones are formed where
(A) Contrasting air masses generally meet
(B) Same air masses generally meet
(C) No air masses meet
(D) None of these
(A) Contrasting air masses generally meet

Question 129.
Which of the following is a real temperate cyclone?
(A) Dynamic cyclone
(B) Thermal cyclone
(C) Secondary cyclone
(D) Both ‘A’ and ‘B’
(A) Dynamic cyclone

Question 130.
The diameter of the temperate cyclone varies from
(A) 160-3200 km
(B) 170-3400 km
(C) 180-3600 km
(D) 190-3800 km
(A) 160-3200 km

Question 131.
The vertical extent of an average cyclone is about
(A) 10-12 km
(B) 12-14 km
(C) 14-16 km
(D) 16-18 km
(A) 10-12 km

Question 132.
Most of the cyclones and anticyclones in the westerly wind belt move from –
(A) East to West
(B) West to East
(C) North to East
(D) South to West
(B) West to East

Question 133.
On an average, diameter of tropical cyclone ranges between
(A) 80-500 km
(B) 80-400 km
(C) 80-300 km
(D) 80-200 km
(C) 80-300 km

Question 134.
Tropical cyclones affect the
(A) Interior areas of continents
(B) Coastal areas of continents
(C) Peninsular areas of continents
(D) Central areas of continents
(B) Coastal areas of continents

Question 135.
Tropical cyclone develops in the regions
(A) of high latitudes
(B) of mid-latitudes
(C) Along the equator
(D) Lying between the tropics of Cancer and Capricorn
(D) Lying between the tropics of Cancer and Capricorn

Question 136.
Tropical cyclones move from East to West under the influence of
(A) Easterlies
(B) Westerlies
(C) Polar winds

Question 137.
________ develops in the Caribbean Sea and North Pacific Ocean during summer months.
(A) Hurricanes or Typhoons
(B) Tropical disturbances
(C) Tropical depressions
(D) Tropical storms
(B) Tropical disturbances

Question 138.
_______ develops frequently in the Bay of Bengal and Arabian sea during the summer season.
(A) Tropical storms
(B) Tropical depressions
(C) Tropical disturbances
(D) Hurricanes or Typhoons
(A) Tropical storms

Question 139.
Match the following :

Question 140.
Tropical cyclones originate over warm oceans having average surface temperature of ______ during summer.
(A) 27° C
(B) 30° C
(C) 33° C
(D) 36° C
(A) 27° C

Question 141.
Tropical cyclone influence the climatic conditions of India between
(A) April and September
(B) April and October
(C) April and November
(D) April and December
(D) April and December

Question 142.
Which of the following is a funnel-shaped cyclone with thick clouds?
(B) Hurricanes
(C) Thunderstorms
(D) Depressions

Question 143.
Auticyclones are vast areas of high pressure with a system of _______ surface winds.
(A) Diverging
(B) Converging
(C) Deformative
(D) Diffusing
(A) Diverging

Question 144.
Auticyclones are indicative of –
(A) Humid weather
(B) Dry weather
C) Rainy weather
(D) Hot and dry weather
(B) Dry weather

Question 145.
The diameter of anticyclones of mid-latitudes is about
(A) 2000 km
(B) 3000 km
(C) 4000 km
(D) 5000 km
(B) 3000 km

Fill in the blanks : 1 Mark

1. Ozone layer was discovered by ________.
2. ‘El Nino’ means ________.
3. Barometer was discovered by ________.
4. A _____ is used to measure air pressure.
5. Air pressure is measured by the unit ________.
6. A ______ is used to measure aire temperature.
7. A ________ is used to measure humidity of air.
8. The westerlies are referred to as roaring forties along the ______ latitude.
9. the westerlies are referred to screaming sixties along the _______ latitude.
10. The _______ is a comparatively calur layer of atmosphere.
11. Van Allen radiation belt can be seen at an altitude of ________.
12. The temperature of the upper part of the mesosphere is about ________.
13. ________ are the chief ozone destroying gases.
14. The radio waves are reflected back to the earth from the ________.
15. Sea breeze blows during ________.
16. The _______ helps to detect rapid change in air pressure.
17. Pompero blows in the valley of river ________.
18. The _______ helps to measure wind speed.
19. In the tropical region, the deserts have been created on the side of the _______ continents.
20. The land breeze blows with the greatest speed during the ________.
21. If pressure gradient increases, wind speed ________.
22. By ferrel’s law, winds deflect towards the in the _______ southern hemisphere.
23. The mediterranearn region received rainfall during ________.
24. the cold wind blowing along the Adriatic Sea coast during winter is called ________.
25. The winds are called ‘snow eaters’.
26. The ________ winds are the heavy winds that descend along the mountain slopes.
27. Connectional rainfall occurs from _______ clouds.
28. Smoke and fog together produce ________.
29. Relative humidity is measured by the instrument called ________.
30. _______ is a rain shadow area in India.
1. Charles Fabry and Henri Buisson
2. Christ child
3. Torricelli
4. Barometer
5. Milibar
6. Thermometer
7. Hygrometer
8. 40°
9. 60°
10. Stratosphere
11. 4000 km
12. (-) 93°C
13. CFCs
14. Ionosphere
15. Day time
16. Barogram
17. Rhine
18. Anemometer
19. Western
20. Early morning
21. Increases
22. Left
23. Winter
24. Bora
25. Chinook
26. Katabatic
27. Cumulonimbus
28. Smog
29. Psychrometer
30. Shillong/Eastern slope of Western Ghats

State True or False : 1 Mark

1. The CO2 absorbs the ultraviolet rays of the sun. [ ]
2. The water vapour present in the atmosphere leads to the scattering of light. [ ]
3. Hydrogen gas concentrates at an altitude of 200-1100 km above the earth’s surface. [ ]
4. The meteors coming from outer space one burnt in the mesosphere of the earth’s atmosphere. [ ]
5. The jet planes fly through the stratosphere. [ ]
6. The thickness of the troposphere is about 8 km near the equator. [ ]
7. CFCs are emitted by refrigerators, air conditioners etc. [ ]
8. The tropopause lies between the stratosphere and mesosphere. [ ]
9. The boiling point of water by the Fahrenheit scale is 212°F. [ ]
10. High pressure prevails in the Arctic circle region. [ ]
11. Orographic rainfall occurs in the windward slope of the mountains. [ ]
12. In tropical regions, cyclones occur due to formation of fronts. [ ]
13. Inversion of temperature occurs in the stratosphere. [ ]
14. A local wind named Fohn blows in Alps mountainous region. [ ]
15. Due to the coriolis force, winds are deflected towards the right in the northern hemisphere, and towards the left in the southern hemisphere. [ ]
16. The 30°-35° latitudes are also known as horse latitudes. [ ]
17. The jet stream influences the monsoon winds. [ ]
18. Low pressure prevails in the centre of anticyclones. [ ]
19. The centre of the cyclone is known as an eye. [ ]
20. The westerlies blow with higher speed in the southern hemisphere than the northern hemisphere. [ ]
21. The anticyclone moves in a clockwise direction in the northern hemisphere. [ ]
22. Cyclones commonly occur in China. [ ]
1. Flase
2. Flase
3. Flase
4. True
5. True
6. Flase
7. True
8. Flase
9. True
10. Flase
11. True
12. Flase
13. True
14. True
15. True
16. True
17. True
18. Flase
19. True
20. True
21. True
22. Flase

Answer in few words : 1 Mark

Question 1.
What is the envelop of air around the earth called?
Atmosphere.

Question 2.
Which gas is needed by green plants?
Carbon dioxide.

Question 3.
Which gas saves us from the harmful Ultraviolet rays ?
Ozone.

Question 4.
Which is the densest layer of the atmosphere ?
Troposphere.

Question 5.
What lies between the stratosphere and mesosphere?
The Stratopause.

Question 6.
Which force is responsible for exertion of atmospheric pressure on the earth’s surface?
The gravitational force of the earth.

Question 7.
What is the horizontal movement of air called ?
Wind.

Question 8.
What is the other name for permanent winds ?
Planetary winds.

Question 9.
Name two winds blowing in opposite directions.
The easterlies or trade winds and the westerlies.

Question 10.
What type of a wind is the monsoon wind ?
Periodic wind.

Question 11.
How is humidity represented ?
In percentage.

Question 12.
By which process does water vapour in the air change into water ?
Condensation.

Question 13.
What is ‘dew’?
Tiny droplets of water that remain suspended in the air.

Question 14.
What is sleet?
Rain and snow falling together.

Question 15.
Name two rain-bearing clouds.
Cumulus and nimbus.

Question 16.
Where does relief rainfall occur?
Windward side of mountains.

Question 17.
Does warm air hold more or less water vapour ?
More water vapour.

Question 18.
Does speedy winds increase the rate of evaporation?
Yes.

Question 19.
What is a saturated air ?
Air that holds the maximum amount of water vapour that it can hold.

Question 20.
Name the instruments measuring humidity.
Hygrometer.

Question 21.
What is measured by a Six’s Maximum and Minimum thermometer?
Maximum and minimum temperatures of a day.

Question 22.
On what does the amount of rainfall depend ?
Moisture content of the air.

Question 23.
What is the side of the mountain facing away from the wind called?
Leeward side.

Question 24.
Which is the most widespread form of rainfall ?
Orographic or relief rainfall.

Question 25.
Where are the meeting of warm and cold fronts common ?
The middle latitudes.

Question 26.
Which season receives most of the rainfall on the earth’s surface?
Summer.

Question 27.
Do the borders or interiors of the continents get more rainfall ?
Borders of the continents.

Question 28.
Which is the hottest part of the earth ?
The equatorial region.

Question 29.
Among on-shore and off-shore winds, which one has less moisture content?
Off-shore winds.

Question 30.
What happens to relative humidity when temperature decreases ?
Relative humidity increases.

## WBBSE Class 10 Geography Solutions Chapter 1.4 Works of Wind

Detailed explanations in West Bengal Board Class 10 Geography Book Solutions Chapter 1.4 Works of Wind offer valuable context and analysis.

## WBBSE Class 10 Geography Chapter 1.4 Question Answer – Works of Wind

Answer in short : 2 Marks

Question 1.
Name the areas where wind action is predominant.
Wind action is predominant in :
(a) Desert regions (tropical and subtropical)
(b) Arid regions adjacent to deserts.
(c) Coastal regions.

Question 2.
On what factors does the erosive actions of wind depend ?
Erosive action of wind depends on :
(a) Wind speed (b) Amount of sand, pebbles etc. carried by the wind, (c) Rock structure of the region (d) Vegetation cover (e) Heat, humidity and amount of rainfall.

Question 3.
Name some famous deserts of the world.
Sahara of Africa, Atacama of Chile, Gobi of Mongolia, Soneran of North America etc.

Question 4.
What is a ventifact ?
In deserts where wind blows from a single direction, large rocks standing in the path of the wind get polished on one side due to abrasion. This one side polished face with sharp edges is called a ventifact.

Question 5.
What is loess?
Plains formed by deposition of fine sand particles carried by wind far away from the place where they belong, are called loess or loess plains.

Question 6.
What is a dreikanter?

In deserts where winds blow from different directions in different seasons, the big rocks lying in the path of the wind get polished on all sides due to abrasion. This multi sided polished faced with sharp edges is called a dreikanter.

Question 7.
What is an oasis ?
In a desert, when sand is deflated from an area continuously, creating a deep hollow or basin, the level of grand water may get exposed. Thus water may seep out from this place forming a shallow water body. This is known as an oasis. A few plants may grow here. A few settlements may also develop.

Question 8.
What is a playa?
Shallow lakes created in depressions surrounded by hills in a desert region are called playa.

Question 9.
The plain land developed adjacent to a pediment by deposition of eroded materials in a deserted region, is called a bajada.

Question 10.
What is a pediment?
When high plateaus or mountains in desert areas are lowered by wind abrasion, the sloping stony plains formed at the foot of the mountain is called a pediment.

Question 11.
What are mesa and butte?

‘Mesa’ means ‘table’ in Spanish. In desert areas, if plateaus are highly dissected by wind erosion, the flat topped landforms thus formed are called mesa. When mesa gets eroded and reduced in size, they are called butte.

Question 12.
What is a gour?
Due to wind abrasion, when the lower parts of big rocks get more eroded than the higher parts, the feature thus formed resembles like a mushroom. This narrow based and broad-topped landform is called a gour.

Question 13.
In desert regions, narrow river valleys created by rainwater are called wadis. They remain dry for most of the year.

Question 14.
What is a ‘dhand’?
In Rajasthan, low depressions created by deflation of sand by wind in desert regions are called ‘dhand’.

Question 15.
Name the northernmost hot desert and the driest hot desert of the world.
Northernmost hot desert – Gobi desert, Driest hot desert – Atacama desert of Chile.

Question 16.
What is the rate of average rainfall in the hot deserts of the world?
Averge rainfall in the hot deserts of the world is around $25 \mathrm{~cm}$ per year.

Question 17.
What kind of ocean currents pass beside the deserts of the world ?
Except for the deserts in Asia, all the other deserts of the diferent continents of the world have cold currents flowing beside them.

Question 18.
What is a ‘Blow-out’ ?
In a desert, when tonnes of sand are blown away by winds, thus creating a hollow or depression which is quite deep, is called a ‘Blow-out’. This is an erosional feature found in a desert. Eg. – Katara in Egypt.

Question 19.
Which desert in the world has the largest moving sand dunes ?
Rub-al-Khali desert of Saudi Arabia, Asia.

Question 20.
What is an inselberg ?
In a desert, the rocky surfaces get reduced by abrasion and attrition of wind action. But, if a resistant rock is present in the path of the wind, it cannot be eroded and lowered equally with the surrounding rock surfaces. Hence, they stand out like isolated or island mountains within the deserts. These are called inselbergs.

Question 21.
What are Barkhans?
The crescent shaped sand dunes created in perpendicular direction to the direction of wind in a desert, are called Barkhans. Eg. – Such crescent sand dunes can be seen in the Sahara and Kalahari deserts in Africa.

Question 22.
What are Seif dunes?
Seif dunes are sand dunes produced in a desert lying parallel to the dirction of wind. They can be several kilometres long but only a few metres wide.

Question 23.
What is an erg ?
The huge deserts formed only of sand particles are known as ergs in Sahara. The same landforms are known as kums in Turkistan. Eg.-Rub-at-khali in Saudi Arabia is the largest erg in the world.

Question 24.
What is reg?
The deserts formed of rock fragments of various sizes are known as reg in Algeria.

Question 25.
What are sand dunes?
The sand particles moved by wind action in a desert and dumped in huge heaps are called sand dunes.

Question 26.
What is a desert pavement?
A desert region composed of unequal pieces of rock fragments is called desert pavement.

Question 1.
What are the reasons for predominant wind action in arid regions?
Although wind blows over the whole of the earth, its action is predominant in arid regions. This is because :

1. No obstacle in wind direction : In desert regions, due to lack of rainfall, there is no or very less vegetation cover. Thus wind blows unhindered with high speed.
2. Loose and exposed soil : Lack of vegetation makes the soil loose and exposed to wind action.
3. High diurnal range of temperature : Great difference between day and night temperature causes rocks to crack and break due to contraction and expansion. This makes the work of the wind easier.

Question 2.
What are the different methods of wind erosion?
The different methods by which the wind erodes are:

1. Deflation : This refers to the process of remaining unsorted dust and sand particles by blowing out by winds.
2. Abrasion : By this method, the sand and rock particles carried by the wind rub, scour, groove, cut and polish any rock surface that comes in its way.
3. Attrition : By this method, the rock and sand particles carried by the wind strike against each other, break and reduce in size.

Question 3.
Differentiate between Yardang and Zeugen.

Question 4.
Mention the factors on which the erosive power of wind depends.
The erosive power of wind depends on – (i) Wind speed (ii) Amount and nature of sand, pebbles and rock fragments carried by the wind (iii) Nature of rock beds (iv) Vegetation cover (v) Heat, humidity and amount of rainfall.

Question 5.
What is a pediment ?
When high plateaus or mountains in deserts are highly eroded and lowered by wind abrasion, the sloping stony plains formed at the foot of the mountains is called a pediment.

Question 6.
Differentiate between a Pediment and a Bajada.

 Pediment Bajada i. Formed by combined work of wind and water at the foot of the mountains due to erosion. i. Formed by combined action of wind and water by deposition of sand, clay, pebbles etc. ii. Lies at the foot of mountains highlands in deserts. (ii) Lies in the stretch between a pediment and playa in a desert. iii. It is a hard rocky region. iii. It is formed by deposition of loose materials like sand, pebbles, gravels etc. iv. Pediments are slightly concave in shape. iv. Bajada are slightly convex and look something like alluvial cones.

Question 7.
What is a blow-out?

The basins or hollows which are formed by sweeping away of loose, light and sandy particles by winds, are called blow-outs or deflation basins. They are known as ‘dhand’ in Rajasthan. The largest blow-out of the world is the Qattara depression in Egypt.

Question 8.
Differentiate between barkhans and seif dunes.

Question 9.
What is loess plain ?
An yellowish sediment produced by wind-blown silt deposition, usually in the size range of 20-50 micrometer, loosly cemented by calcium carbonate is called loess. The flat regions covered by such deposits are called loess plains. This helps to make farm land very fertile.

Question 10.
Why wind action also active in the coastal regions ?
Action of wind is very active in desert area. But it is also active in coastal area, because :
1 . Open and extensive coastline helps to blow the sea breeze towards the land with no obstraction and cause erosion of coastal area.
2. Sea waves are help to break the rocks of coastal area into small granules which can be then easily blow away by the wind.
3. Uninterrupted wind blown through the coastal area carried sand prevent in the coast and formed landforms like sand dunes in the coastal region.

Question 11.
What is an Inselberg ?

The German term inselberg means ‘Island mountain’. They are outstanding, rounded, steep-sided residual hills rising abruptly from nearby eroded flat surface. Their height may vary from 10-300 m.

Question 12.
Name the landforms formed by combined action of wind and water.
Landforms formed by combined action of wind and water are : wadi, playa, pediment and bajada.

Question 13.
Name the regions where wind action is predominant in creation of new landforms.
The regions where wind action is predominant in creation of new landforms are:

1. Deserts (Tropical and sub-tropical regions)
2. Semi-arid and dry regions adjacent to deserts.
3. Coastal areas.

Question 14.
How is sand particles formed in desert regions ?
In deserts, due to high temperature fluctuations between day and night, the barren exposed rocks are severely expanded and contracted regularly. This causes breaking of the rocks into smaller parts and finally leads to the formation of sand. The pebbles and fragments of rocks borne by the wind hit against the rocky walls of mountains, hills or other land surfaces. This causes high rates of erosion, and thus leads to formation of sand. Presence of hard minerals in the broken rock fragments cause exploding action when they colide with the rock surfaces. This also helps in creation of sand.

Answer in details : 5 Marks

Question 1.
Name and describe the landforms formed by wind depostion.
The different landforms formed by wind deposition are :
(i) Longitudinal or Seif dunes : Low but long ridges of sand particles lying parallel to the wind direction are called seif dunes. They may be 40-70 m. in height, about 100 m in width, and a few kilometres in length.

(ii) Transverse dunes: When dunes are formed perpendicular or transversely to the wind direction, they are called transverse dunes. They are common in deserts where sand supply is abundant and wind speed is moderate.

(iii) Barkhans : Crescentshaped sand dunes that receive wind from only one direction are called barkhans. They have two horns opposite to the wind direction.
(iv) Loess : Fine sand particles, carried by winds and deposited far away from their place of origin, forming extensive plants are called loess.

Question 2.
What are the main causes of spread of deserts or desertification?
The main causes of desertification are :
(a) Physical causes :

1. Drought : Regular and repeated droughts may damage the soil permanently, preventing any vegetative growth, hence bringing in desertification.
2. Climatic changes : Green house effect and global warming may affect the climate of an area and advance desertification.
3. Soil erosion : Removal of top soil may also cause desertification.
4. Presence of mountains : Presence of mountains may obstruct moisture-laden winds to cause rainfall. Hence deserts may be created in the rain shadow areas.

1. Over-grazing : Over-grazing may remove the vegetative cover of the soil permanently, and cause desertification.
2. Over-cultivation : Unscientific cultivation may cause removal of nutrients from the soil and cause further extension of deserts.
3. Uncontrolled irrigation : Over-irrigation may cause soils to become saline, loose fertility and tend to turn into deserts.
4. Deforestation : Cutting down of trees remove vegetative cover and cause desertification.

Question 3.
What are the methods of controlling desertification?
The process of desertification is very difficult to stop totally. But certain steps may be taken for its control :

1. Controlled grazing : Grazing should be controlled, especially in arid and semiarid regions.
2. Cultivation : Cultivation of drought resistant crops must be encouraged near deserts.
3. Afforestation : Trees should be planted to cover up exposed areas.
4. Irrigation : Controlled irrigation helps to improve soil quality.
5. Others : Other steps that can be taken are – rain water harvesting, preventing salinity of soil, proper planning of land use, increasing consciousness among people etc.

Question 4.
What are the causes of desertification of Sahara? What are the remedial steps taken?
Sahara in Africa is the largest hot desert of the world, covering about 91,00,000 sq km area.
Causes of desertification : (i) Extreme sand storms (ii) Lack of rainfall due to global warming (iii) Reduction of agriculture at the borders of the desert.

Preventive measures :

1. The Federal state and the govt. of Nigeria has taken up annual tree planting programmes. Free plants are distributed to be planted in agricultural fields and houses.
2. Heavy reforestation programmes are taken up in dry areas of Mali, Mauritania, Niger, Sudan, Senegal, Chad, Ethiopia etc.
3. Involvement of ladies, youth and students in reforestation and awareness programmes.

Question 5.
Mention the causes of spread of the Thar desert and the preventive measures taken.
The Thar desert spreads over 2.34 million sq. km. in India over west Rajasthan, Gujarat, south west Punjab and parts of Haryana.

Causes of spread of desert : (i) High speed winds (ii) Large moving sand dunes (iii) High diurnal range of temperature (iv) Low rainfall (v) High rate of evaporation.
Preventive measures : (i) Reforestation is being done on the hill slopes in this region according to several government programmes. (ii) Artifical grasslands are being created to prevent movement of sand dunes in Barmer, Jaisalmer, etc. (iii) Trees that grow fast, are being planted to meet the demand of fuel wood of local people in Jaisalmer, Jhuijhunu etc.(iv) The Rajasthan canal has been constructed to irrigate and reclaim infertile land.

Question 6.
Name and describe three landforms created by erosive action of wind.
The landforms created by erosive action of wind are :

(i) Gour : When the lower portions of a huge rock mass is eroded away much more compared to the upper portions, the landform thus formed resembles a mushroom. Such top heavy features are called ‘Gour’.
(ii) Yardang : When hard and soft rocks lie in bands in vertical direction to the direction of the wind the softer rocks get eroded very fast, while the harder rocks act like resistances and get less eroded. The harder rocks have rugged surfaces. These are called ‘Yardangs’.

(iii) Zeugen : When hard and soft rocks lie in bands perpendicular to the direction of wind, the soft rocks are eroded away very fast. The hard rocks stand out like broad topped and narrow-based landforms. These are called ‘Zeugens’.

Question 7.
Describe the different landforms formed by combined action of wind and water in desert areas.
The different landforms formed by the combined action of water and wind in a desert region are :
(i) Wadi : In deserts sudden torrential rains lead to formation of valleys through which the collected rain water may flow like a river. In dry season, these valleys also remain dry.

(ii) Playa : Playas are small lakes found in deserts. They are highly saline and the water cannot be used for agricultural or household purposes.
(iii) Pediment : Pediment refers to the eroded and lowered plainlands that lie at the foot of the mountains.

(iv) Bajada : Bajada refers to the deposition of materials, brought down by wind as well as water and deposited beyond the pediment.

Multiple Choice Question (MCQ) : 1 Mark

Question 1.
Loess is commonly formed by deposition of
(A) Silt by wind
(B) Sand by wind
(C) Silt by rivers
(D) Dust by volcanoes
(B) Sand by wind

Question 2.
The crescent shaped sand dunes are called
(A) Barkhans
(B) Seif
(C) Yardang
(D) Arete
(A) Barkhans

Question 3.
Landforms, not associated with wind erosion is
(A) Rock pedestal
(B) Zeugen
(C) Yardang
(D) Dunes
(D) Dunes

Question 4.
Pediments are formed in
(A) Arid regions
(B) Coastal regions
(C) Glacial regions
(D) Valley regions
(A) Arid regions

Question 5.
Gour can be found in
(A) Coastal area.
(B) Arid region
(C) Glaciated region
(D) Island area
(B) Arid region

Question 6.
Lakes formed within sand dunes are called
(A) Dhands
(B) Dhrians
(C) Playas
(D) Shots
(A) Dhands

Question 7.
(A) Mountain Valley
(B) Flower Valley
(C) Depressional Valley
(D) Dry Valley
(D) Dry Valley

Question 8.
(A) Erosional plain formed by wind
(B) Depositional plain formed by wind and water
(C) Erosional plain formed by river
(D) Depositional plains formed by glaciers
(B) Depositional plain formed by wind and water

Question 9.
Yardang is formed by
(A) Glacial deposition
(B) Marine deposition
(C) Wind erosion
(D) Sea erosion
(C) Wind erosion

Question 10.
Isolated hard resistant rocks scatterd in plain deserts are called
(B) Inselbergs
(C) Drumlins
(D) Spur
(B) Inselbergs

Question 11.
The steep-sided, deeply undercut, overhanging rock ridges separated from one another by long grooves in desert floors of relatively softer rocks are called
(A) Dreikanters
(B) Ventifacts
(C) Zeugens
(D) Yardangs
(D) Yardangs

Question 12.
Wind windows and window bridges are ______ land forms.
(A) Transportational
(B) Erosion
(C) Depositional
(D) None of these
(B) Erosion

Question 13.
Accumulation of sands between obstacles are called
(B) Sand drifts
(C) Sand dunes
(D) Ripple marks
(B) Sand drifts

Question 14.
The wind-borne materials deposited beyond the limits of the deserts by wind action are called
(A) Sand dunes
(B) Loess
(C) Ripple marks
(D) Barkhans
(B) Loess

Question 15.
The loess formation in China is most prominent in
(A) North China
(B) East China
(C) South China
(D) West China
(A) North China

Question 16.
Wind erosion in the arid and semi-arid regions is assisted by
(A) Chemical weathering
(B) Mechanical weathering
(C) Biological weathering
(D) Differential weathering
(B) Mechanical weathering

Question 17.
Wind erosion is largely controlled and determined by
(A) Wind velocity
(B) Compositions of rocks
(C) Nature of Vegetation
(D) All of these
(D) All of these

Question 18.
The process of removing, lifting and blowing away dry and loose particles of sads and dusts by wind is called
(A) Deflation
(B) Abrasion
(C) Attrition
(D) Corrosion
(A) Deflation

Question 19.
Which of the following rocks are called ‘gara’ in Sahara?
(A) Dreikanter
(B) Dunes
(C) Stone lattice
(D) Mushroom rocks
(D) Mushroom rocks

Question 20.
Wind transports materials by the process of
(A) Suspension
(B) Saltation
(C) Traction
(D) All of these
(D) All of these

Question 21.
The mineral abundantly found in sand duhes is
(A) Quartz
(B) Kaolin clay
(C) Feldspar
(D) Clay
(A) Quartz

Question 22.
The dunes formed along coasts and margins of deserts are called
(A) Longitudinal dunes
(B) Transverse dunes
(C) Bankhan dunes
(D) Parabolic dunes
(B) Transverse dunes

Question 23.
The sand dunes formed parallel to wind direction are called
(A) Transverse dunes
(B) Barkhan dunes
(C) Parabolic dunes
(D) Longitudinal dunes
(D) Longitudinal dunes

Question 24.
Which of the sand dunes have two horns ?
(A) Nebkha
(B) Barkhan
(C) Seif
(D) Transverse dunes
(B) Barkhan

Question 25.
The example of the most significant wind blown deposits is
(A) Sand dunes
(B) Loess
(C) Ripple marks
(D) Playa
(B) Loess

Question 26.
Loess is known as ‘Limon’ in
(A) France
(C) Australia
(D) China
(A) France

Question 27.
‘Inselberg’ was first named by
(A) W. M. Davis
(B) L. C. King
(C) R. L. Parker
(D) R. A. Bagnold
(B) L. C. King

Question 28.
Seif dunes were first named by
(A) L.C.King
(B) W. Penck
(C) W. M. Davis
(D) R. A. Bagnold
(D) R. A. Bagnold

Question 29.
The dry river channels in arid regions are called
(B) Bolson
(C) Salina
(D) Loess

Question 30.
The salt lakes found in arid regions are called
(A) Bolson
(C) Playa
(D) Dhand
(C) Playa

Question 31.
The shifting dunes of Rajasthan are locally known as
(A) Dhrian
(B) Barchan
(C) Loess
(D) Blow out
(A) Dhrian

Question 32.
Cresentic dunes are called
(A) Seif
(B) Barchan
(C) Loess
(D) Blow out
(B) Barchan

Question 33.
Pediments are formed by the ______ works of wind and temporary stream.
(A) Erosional
(B) Transportational
(C) Depositional
(D) Erosional and Depositional
(A) Erosional

Question 34.
The hard rocks standing like dames or hills is a desert are called
(A) Mushroom rock
(B) Inselbergs
(C) Yardangs
(B) Inselbergs

Question 35.
‘Gara’ is formed by the action of
(A) River
(B) Glacier
(C) Wind
(D) Waves
(C) Wind

Question 36.
(A) Akle dunes
(B) Seif
(C) Gara
(B) Seif

Question 37.
Marusthali means
(C) A land of heavy rainfall
(D) Lack of camels.

Question 38.
Mesas are eroded further to form
(A) Zeugen
(B) Butle
(C) Inselberg
(D) Yardang
(B) Butle

Question 39.
The dome shaped low hills present is the peneplain regions are called-
(B) Gara
(C) Yardang
(D) Till

Question 40.
In peneplain, low lying hill of hard rocks remains as residual landform is called
(A) Yardang
(B) Zeugen
(C) Sand dunes
(D) Inselberg
(D) Inselberg

Fill in the blanks : 1 Mark

1. The playa lakes in the arid regions of Africa are known as _______.
2. The playa lakes in the desert region of Rajasthan are known as _______.
3. The crescent-shaped sand dunes lying perpendicular to the wind direction are called _______.
4. The vast sandy deserts in Sahara, lacking any vegetation are called _______.
5. The playa lakes are known as _______ in the desert regions of Mexico.
6. _________ is the largest sandy desert of the world.
7. _________ dunes are created from seif dunes.
8. The desert research centre of India is located at _______.
9. The term ‘dreikanter’ means _______.
10. _______ is a cold desert in India.
11. Loess comes from a German word meaning _______.
12. _______ has its origin in the Arabic word meaning ‘Sword’.
13. Thick loess deposits are found in _________ in India.
14. The desert lakes in Sahara are known as _______.
15. Oases are formed by ________ action of wind.
1. Shots
2. Dhand
3. Barkhans
4. Erg
5. Bolson
6. Rub-at-khali desert in Saudi Arabia
7. Barkhan
8. Jodhpur
9. Three-sided
11. Loose materials
12. Seif
13. M.P.
14. Shalts
15. Erosion

State True or False : 1 Mark

1. Barkhans mean crescent-shaped dunes. [ ]
2. The largest desert of the world is Sahara. [ ]
3. The action fo wind is mostly noticed in high mountains [ ]
4. Barkhans are formed by erosional action of winds. [ ]
5. The sand dunes along the coastal region of Kerala are called terres. [ ]
6. The largest deflation hollow of the world is Qatara. [ ]
7. The driest desert of the world is Sahara. [ ]
8. The rocky part of the Sahara desert is called hamada. [ ]
9. The region between two seif dunes is called gasi. [ ]
10. Oases are created due to abrasion of wind. [ ]
11. Pediment is a type of plain. [ ]
12. The loward slope of the ventifact is smooth and sharp. [ ]
13. The landforms looking like mushrooms found in deserts are called yardang. [ ]
14. The Salt water lakes of deserts are called wadies. [ ]
15. The Taklamakan Desert lies in China. [ ]
16. ‘Mesa’ means ‘Chair’ in Spanish. [ ]
1. True
2. True
3. False
4. False
5. True
6. True
7. False
8. True
9. True
10. True
11. True
12. False
13. False
14. False
15. True
16. False

Match the following :

 List 1 List 2 A. Sahara i. Asia B. Gobi ii. Africa C. Salina iii. South America D. Barkhan iv. North America E. Soneran v. Kirghiz, Steppe region F. Atacama vi. Playa lake

 List 1 List 2 A. Sahara ii. Africa B. Gobi i. Asia C. Salina vi. Playa lake D. Barkhan v. Kirghiz, Steppe region E. Soneran iv. North America F. Atacama iii. South America

Answer in few words : 1 Mark

Question 1.
What are sandy deserts known as ?
Erg.

Question 2.
What are the moving sand dunes of Rajasthan called ?
Dhrians.

Question 3.
What are rocky deserts known as ?

Question 4.
What are ‘gours’ also known as ?
Gara, or mushroom rocks or rock pedestals.

Question 5.
What are inselbergs?
Outstanding rounded steep-sided residual rocks or hills in deserts.

Question 6.
What are deflation basins ?
Hollows created in deserts by sweeping away or deflation of sand by wind.

Question 7.
What are dunes?
Heaps of sand formed by wind deposition in deserts.

Question 8.
What are Barkhans?
Crescent shaped sand dunes.

Question 9.
Which is the largest ‘hot’ desert of the world ?
Sahara desert in Africa.

Question 10.
Where does the Thar desert lie in India ?
West Rajasthan, Gujarat, South-western Punjab and parts of Haryana.

## WBBSE Class 10 Geography Solutions Chapter 1.3 Works of a Glacier

Detailed explanations in West Bengal Board Class 10 Geography Book Solutions Chapter 1.3 Works of a Glacier offer valuable context and analysis.

## WBBSE Class 10 Geography Chapter 1.3 Question Answer – Works of a Glacier

Answer in short : 2 Marks

Question 1.
What is a glacier?
A glacier is a moving body of snow and ice which under the influence of gravity moves slowly over the land downslope.

Question 2.
What is an avalanche?
Huge amount of snow and ice breaking off and falling along steep slopes of mountains is called an avalanche.

Question 3.
Classify glaciers.

Question 4.
What are continental glaciers?
In higher latitudes, glaciers cover almost the whole continent due to immense cold. These are called continental glaciers. Eg. – glaciers in Antarctica, Greenland, Iceland etc.

Question 5.
What are valley glaciers?
Glaciers that flow through mountain valleys in higher latitudes and higher altitudes are called valley glaciers. Eg-Siachen glacier in the Karakoram range.

Question 6.
What are piedmont glaciers?
When glaciers of higher latitudes reach the foothills of mountains, they still don’t melt due to immense cold. These are called piedmont glaciers.

Question 7. a
What is an arete?
The thin steep ridge of the mountain lying between two adjacent corries is called an arete.

Question 8.
What is a pyramid peak ?

When three or more corries are created on the surface of the same mountain, the sharp edged landform thus created looks like a pyramid. This is called the pyramid peak.

Question 9.
What are eskers?

Long ridge of material deposited parallel to the direction of flow of glacial melt water is called an esker.

Question 10.
What are erratics?
When glaciers melt, the boulders get deposited in an area where they may be a total mismatch with the surroundings. These are called erratics.

Question 11.
What are outwash plains?

Materials washed out by glacial melt water and deposited in a variety forms are called outwash plains.

Question 12.
What are kettle lakes?
The melt water from glaciers may get accumulated in holes created in outwash plains due to melting of detached mass of ice that might have been left partly or wholly buried. These are called kettle lakes.

Question 13.
What is an iceberg ?
The huge masses of ice floating in the oceans are called icebergs. If continental glaciers spread till the coastline, the ocean currents cause the ice at the edge of the glaciers to break and float in the water. 8/9th parts of the icebergs lie beneath the water and only 1/9th part is seen above the surface.

Question 14.
What is snowline?
The imaginary line above which the snow never fully melts or below which line, snow starts to melt is called mountain. The height of this line varies one climatic region to another.

Question 15.
What do you know about end moraines ?
Moraines refers to the deposition by glaciers at the foothill region. When the shape of this depositions are horse-shoe shaped and have concave slopes, they are called end moraines.

Question 16.
What is paternoster lake?
A glacier encountering weaker rocks at its base, will be able to erode deeper than when it experiences harder, less erodable rocks. As the glacier melts, lakes form where weaker rock was excavated, this lakes are called paternoster lake.

Question 17.
What is a nunatak?
In a continental glacier, near the edges, where the ice layers are not so thick, some hills or domes may rise above the snowy surface, which have no deposition of snow on them. These bare rocky outcrops within the glacial snow are called nunataks.

Question 18.
What are the characteristics of continental glaciers ?
The characteristics of continental glaciers are :

1. These glaciers are larger in volume and size than other types of glaciers.
2. These glaciers are thicker at the middle and thinner at the edges. Hence they look like domes.
3. Depth of these glaciers is greater compared to other glaciers.
4. The direction of flow of continental glaciers is from the centre towards the edges from all sides.
5. The edges of these glaciers break off to form icebergs.

Question 19.
What is a snout?
In valley glaciers, the mass of ice flows through specific valleys. The walls and base of the valley provide immense friction and try to prevent the ice from flowing. Hence, the middle part of the glacier, which experiences less friction, seem to move forward. This appears like a tongue-shaped feature. This is known as the snout of the glacier. The snow of the snouts gradually melts to give rise to rivers.

Question 20.
Why are pyramidical peaks also called ‘horns’?
The Matterhorn peak in Switzerland is an example of a pyramid peak. Hence, following the name of the peak, the pyramidical peaks are also called horns.

Question 21.
What is boulder clay ?
Glaciers deposit unassorted load or debris when they start melting. If big boulders get deposited over a field of sandy and clayey deposits, the landform is called boulder clay or till.

Question 22.
What do you mean by a ‘Basket of eggs’ topography ?
When numerous drumlins are formed due to glacial deoposition very close to each other, the region looks like numerous eggs placed in a basket. Hence, such a topograhy is called a ‘Basket of eggs’ topography.

Question 23.
What is an Agamuk ?
The huge chunks of boulders and rock fragments deposited near mountains due to depositional work of glaciers form a typical landform called Agamuk.

Question 24.
What is an ice sheet?
An ice sheet is a large mass of ice that covers the surrounding terrain and is greater than 50,000 km<sup>2</sup>. This is also known as continental glacier.

Question 25.
What is crag and tail ?
In a glaciated region, if any huge hard block of rock lies inbetween soft rocks, the glacier erodes the softrock while climbing up the huge hard rock. The soft rocks lying at the back of the hard rock from where the glacier descends, does not get eroded much compared to the front. Thus, the huge hard rock standing out is known as the crag and the band of softrock lying at the back is known as the tail.

Question 26.
What do you mean by ice age?
Ice age is a period of long-term reduction in the temperature of the earth’s surface and the atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers.

Question 27.
What are neve and firn?
Neve is a granular, porous type of snow which has been partially melted, refrozen and compacted, leading to the formation of glacial snow. This forms the surface of the upper-end of the glacier. Firn is partially compacted neve. It is a type of snow that has been left over from the past seasons and has been recrystallized into a substance denser than neve. It is intermediate between snow and glacial ice.

Question 1.
How is a glacier formed ?
In higher latitudes and higher altitudes, the regions above the snowline accumulated much snow due to immense cold. This snow is gradually compacted and converted to ‘neve’. This storage of ice gradually flows down the slope of land, hence forming a glacier.

Question 2.
What is a Bergschrund ?
A Bergschrund is a long narrow crack developed at the source of the glacier. This is created when the mass of ice tends to flow down due to gravity and the mountain walls tend to hold back the ice due to friction.

Question 3.
Mention the methods by which a glacier erodes.
The glacier can erode by the following methods:
(a) Plucking : As the glacier starts moving, the solid mass of ice plucks out any protruding rock that comes in the way. This is called plucking.
(b) Abrasion : As the glacier moves forward, the already plucked rock fragments rolls against the floor and walls of the valley and also against each other. This makes the rock fragments rounded and smooth. This is called abrasion.
(c) Frost Wedging : When glacial ice melts partially, the water percolates into the adjacent cracks and joints. Once again when it freezes, the volume of water (as ice) increases and exerts pressure on the walls of the cracks. Thus rocks break apart. This is called frost wedging.

Question 4.
What is a fjord?
In higher latitudes, the glaciers near sea coasts erode their valleys so deeply that the base of the valleys seem to get lowered than the sea level as well. These regions get filled up with sea water and the higher walls look like gradually submerged ridges. Such a reigion is called a fjord. Eg-‘Sogne’ fjord of Norway.

Question 5.
Why are waterfalls common in hanging valleys ?
In mountainous regions, where the smaller glaciers meet the main glacier, the main glacier curves deeper valleys than the smaller glaciers. When the ice melts, these smaller glacier valleys seem to hang over the main glacial valley, which is quite deeper. When water flows through the hanging valleys into the main valley, they obviously form waterfalls.

Question 6.
Why is the position of the snowline flexible ?
The presence of permanent snow varies or depends on several factors – eg. latitudes, height, slope, season, wind direction, wind speed, heat content etc. Change in any of the factors results in melting of ice or falling of new snow. Hence, the previous snow line may get changed. Thus the snowline is flexible.

Question 7.
What is a drumlin ?
Drumlins are long narrow deposition of boulders and clay brought down by glaciers at the foot hills of the mountains. They look like inverted boats. They are also known as ‘Basket of eggs’ topography.

Question 8.
Classify moraines.
Moraines are the depositions of rock fragments and clay brought down by glaciers and deposited along their path of movement. They can be classified as :

(a) Side moraines : When the debris is deposited along the side walls of the glacial valley, they are known as side moraines.
(b) Medial moraines : When two glaciers meet, the side moraines of both the glaciers on one side tend to merge with each other. This deposition continues for a considerable distance and lies in the middle of the newly joint glacier.
(c) End moraines : When debris is deposited at the end of the glacier after which it starts melting into water, it is known as end moraines.

Question 9.
Differentiate between Roche moutonnee and Drumlin.

 Roche moutonnee Drumlin i. This looks like a high heap of rocks. i. This looks like an egg basket or inverted boat. ii. This is an erosional landscape of glaciers. ii. This is a depositional landscape of glaciers. iii. The side along the flow of the glacier is smooth, while the other side is rough. iii. The side along the flow of the glacier is rough and the other side is smooth. iv. This may lie single. iv. This usually lies in groups.

Question 10.
Differentiate between Continental and Mountain Glaciers.

 Continental Glaciers Mountain Glaciers i. This occupies huge landmasses and spreads over almost the continents. i. This occupies mountain valleys of high altitudes and high latitudes. ii. Largest of all glaciers. ii. Comparatively smaller glaciers. iii. Usually depth of ice is very high. iii. Usually have lesser depth of ice. iv. Eg. – Lambert in Antarctica. iv. Eg. – Gangotri, Yamunotri etc. of the Himalaya.

Question 11.
What are crevasses?

Crevasses are cracks formed on the surface of glaciers. If the glaciers flow over a uniform slope throughout, crevasses are not formed. But if the surface underlying the snow is rugged and undulating, the glacier has to ride the higher parts and slope down the lower parts. Thus, a great force of tension works on the snow. This creates the crevasses.

Question 12.
On what factors does the erosive power of glaciers depend?
The erosive power of glaciers depend on the following factors :

1. Speed : If the glaciers have greater speed, they have greater rate of erosion.
2. Depth of ice : Greater the depth of ice of the glacier, greater is its erosive power.
3. Permanency of the glacier : If the glacier remains so for a long period of time, its rate of erosion will also be much greater.

Question 13.
What is ‘Snowline’?
Snowline is the boundary that marks the existence of permanent snow beyond a certain altitude due to very cold atmospheric conditions. According to F. J. Monkhouse, snowline indicates the lowest edge of continuous snow cover.

Question 14.
Name the different landforms created by glaciers in higher altitudes.
The landforms created by glaciers on higher altitudes are – corrie or cirque, cirque lakes, arete, pyramid peak or horn, hanging valleys, spurs, fjords etc.

Question 15.
Name the different landforms created by glaciers in lower altitudes.
The landforms created by glaciers on lower altitudes are – roche moutonnee, crag and tail, drumlin, esker, agamuk, till, kettle, kettle lakes, outwash plains etc.

Question 16.
Differentiate between a river valley and glacial valley.

 River Valley Glacial Valley i. V-shaped or I-shaped valleys are formed by rivers. i. Glaciers form U-shaped valleys. ii. In upper course, the down cutting of valley is more than side cutting. ii. In glacial valleys, side cutting is more compared to down cutting. iii. The valley walls are steep and the base is narrow. iii. The valley walls are steep and the base is broad. iv. Valleys in most regions are called gorges and those in dry regions are called canyons. iv. Glacial valleys are of different types, eg-Alipne, Iceland type, mixed type etc.

Answer in details : 5 Marks

Question 1.
Explain the formation of corrie, arete and pyramidal peak by glacial erosion.

Corrie, arete and pyramidal peak are landforms formed by mountain glaciers in the higher altitudes near the source of the glaciers.
(a) Corrie or cirque : Corrie or cirque in an armchair shaped or amphitheatre or spoon shaped depression created by the glacier on the higher slopes of the mountains from where the glacier starts flowing.
(b) Arete : The steep narrow sharp ridge like landform lying between two adjacent cirques are known as arete.
(c) Pyramidal peak : If three or more glaciers descend from the same mountain, formation of cirques and arete all around give a sharp and steep look to the peak, resembling a pyramid. This is known as the pyramidal peak.

Question 2.
Describe the formation of hanging valley and Roche moutonnee.
Hanging Valley : In high altitudes, many small glaciers may come and meet with a large or main glacier. The smaller glaciers have lesser ice content and hence lesser erosive capacity than the main glacier. Hence, the valleys curved by smaller glaciers are lesser in depth than the main glacier. When the ice melts, these smaller glacial valleys seem to hang over the main glacial valley. This kind of a landform is called a hanging valley.
i
Roche moutonnee : If any resistant rock lies in the path of a glacier, the flowing ice and rock fragments polish the surface of the resistant rock on the side in the direction of flow of the glacier. The other side of the rock is scooped, scraped and plucked by the rock fragments and ice, thus making the surface rough and rugged, as the glacier moves forward. Such a landform, resembling the ‘back of a sheep’ is called a roche moutonnee.

Question 3.
Describe some landforms formed by glacial deposition.
The landforms formed by glacial deposition are :

i. Moraines : Any landform formed by depositions of valley and continental glaciers is called moraines. The moraines can be mainly of three types – (a) Moraines deposited along side of glacial valley floor are called lateral moraines. (b) Where two lateral moraines of adjacent glaciers combine, the deposition lying in the middle of the main glacier is called medial
moraine. (c) Moraines deposited at the end of a glacier are called terminal or end moraines.

ii. Eskers : Long ridges of material deposited parallel to the direction of the flow of glacial melt water are called eskers.

iii. Erratics : These are depositions of boulders and rock fragments in an area where they are a total mismatch with the surroundings.

iv. Drumlins : These are low elongated hills formed by glacial deposits. They are also called ‘Basket of eggs’ topography.
v. Kames: These are small rounded hillocks of sand and gravel.
vi. Outwash plains : These are materials

Question 4.
Compare and contrast between the works of river and glacier.

 Item Works of river Works of glacier (i) Definition A flowing body of water coming downslope from high lands to lowlands due to gravity, meeting any sea, ocean, lake etc. is called a river. A flowing body of huge amount of ice coming downslope from a mountainous region due to gravity is called a glacier. (ii) Speed Rivers have great speed in the mountainous region, medium speed in plateau region and less speed in the plains. Glaciers have yery low speed throughout the course. (iii) Path River finds its path avoiding any obstacle by taking curves. Glacier tends to flow in a straight path removing any obstacle that comes in the way. (iv) Working capacity Depends on slope of land, quality of rocks in the channel and water content. Depends on amount of ice, slope of land and quality of rocks in the channel. (v) Works Erosion, transportation and deposition. Erosion, transportation and deposition. (vi) Methods of erosion Hydraulic action, corrasion or abrasion, attrition, solution. Plucking, abrasion and frost wedging. (vii) Type of erosion Mechanical and chemical Only mechanical (viii) Valley V-shaped U-shaped. (ix) Erosional landforms Gorge, canyon, waterfalls, pot hole, plunge pool, interlocking spur etc. Corrie, arete, pyramid peak, hanging valley, roche moutonnee, crag and tail etc. (x) Depositional landforms Alluvial fan and cone, flood plain, natural levee, delta, sand bar, braided channel etc. Moraines, eskers, kames, drumlin, erratics, outwash plains etc.

Multiple Choice Question (MCQ) :

Question 1.
Which of these regions has continental glaciers ?
(A) Himalaya
(B) Alps
(C) Andes
(D) Greenland
(D) Greenland

Question 2.
Which landform is created by glacial erosion ?
(A) Arete
(B) Moraine
(C) Drumlin
(D) Plunge pool
(A) Arete

Question 3.
Which landform is created by glacial deposition ?
(A) Cirque
(B) Hanging Valley
(C) Arete
(D) Moraine
(D) Moraine

Question 4.
Cirques are
(A) Basins formed by river erosion
(B) Basins formed by wind erosion
(C) Vast amphitheatre like basin curved by glaciers
(D) None of these
(C) Vast amphitheatre like basin curved by glaciers

Question 5.
Kettle holes are
(A) Depressions made by melting ice
(B) Depressions found at foot hills
(D) None of these
(A) Depressions made by melting ice

Question 6.
Horn is created by
(A) One cirque
(B) Two cirques
(C) Cols
(D) Aretes
(D) Aretes

Question 7.
Moraines are
(A) Depositions by rivers
(B) Depositions by glaciers
(C) Depositions by winds
(D) None of these
(B) Depositions by glaciers

Question 8.
Drumlines are
(A) Boat-shaped depositions
(B) Narrow vallys
(C) Armchair shaped depression
(D) Pyramid peak
(A) Boat-shaped depositions

Question 9.
Kames are
(A) Rift valleys
(B) Sand dunes
(C) Steep hills
(D) Long irregular hills formed by glacial deposition
(D) Long irregular hills formed by glacial deposition

Question 10.
Outwash plain is
(A) Debris deposited by river
(B) Formed by silt deposition
(C) Debris deposited by ice at valley bottom
(D) None of these
(C) Debris deposited by ice at valley bottom

Question 11.
Which landform is created by glacier?
(A) Inselberg
(B) Meander
(C) Pyramidal peak
(D) Gour
(C) Pyramidal peak

Question 12.
Basket of eggs topography is related with
(A) Eskers
(B) Drumlins
(C) Outwash plains
(D) Corrie
(B) Drumlins

Question 13.
Fjord coast is formed by
(A) Action of sea waves
(B) Submergence of river valleys
(C) Submergence of glacial valleys
(D) Action of wind
(C) Submergence of glacial valleys

Question 14.
Hanging Valleys are formed by
(A) Mountain glaciers
(B) Continental glaciers
(C) Piedmont glaciers
(D) Coastal glaciers
(A) Mountain glaciers

Question 15.
Glacial valley is
(A) I-shaped
(B) U-shaped
(C) V-shaped
(D) Y-shaped
(B) U-shaped

Question 16.
The altitude over which snow never melts is called
(A) Snowline
(B) Glacier
(C) Tree line
(D) Cold wall
(A) Snowline

Question 17.
Who commented – ‘A glacier is a mass of snow and ice that moves slowly over the land away from its placeof accumulation?
(A) Worcester
(B) Flint
(C) Lobeck
(D) Thombry
(A) Worcester

Question 18.
The biggest glaciers on the earth’s surface are called
(A) Continental glaciers
(B) Cirque glaciers
(C) Niche glaciers
(D) Ice sheets
(D) Ice sheets

Question 19.
Antarctica and greenland ice sheets are the examples of
(A) Mountain or valley glaciers
(B) Piedmont glaciers
(C) Continental glaciers
(D) Ice shelf
(C) Continental glaciers

Question 20.
Which of the following is a floating thick ice sheet or ice cap attached to the coast?
(A) Ice field
(B) Ice shelf
(C) Valley glacier
(D) Cirque glacier
(B) Ice shelf

Question 21.
The destruction of glacier front due to melting of ice consequently due to increase of temperature is called
(B) Stagnation of glacier
(C) Ablation of glacier
(D) None of these
(C) Ablation of glacier

Question 22.
The glacier erodes its bed and side walls with the help of tools of erosion by the mechanism of
(A) Attrition
(B) Abrasion
(C) Corrosion
(D) Plucking
(B) Abrasion

Question 23.
‘Head wall’ is a component of
(A) Tarn
(B) Nunatak
(C) U-shaped valley
(D) Cirque
(D) Cirque

Question 24.
‘Corrie’ is the name of _____ in Scotland.
(A) U-shaped valley
(B) Arete
(C) Horn
(D) Cirque
(D) Cirque

Question 25.
The line above which snow never meets in the high altitudes is called
(A) Snow line
(B) Glacier
(C) Iceberg
(D) Blow out
(A) Snow line

Question 26.
______ part of an iceberg floats above the water surface
(A) 8 / 9
(B) 2 / 9
(C) 1 / 9
(D) 9
(C) 1 / 9

Question 27.
Continental glaciers are seen is
(A) Himalayas
(B) Alps
(C) Andes
(D) Antarctica
(D) Antarctica

Question 28.
The landform between two adjacent cirques is called
(A) Roches moutonnee
(B) Arets
(C) Pyramid peak
(D) Eskar
(B) Arets

Question 29.
_____ is an example of an pyramidal peak
(A) Mont Blanc
(B) Matterhorn
(C) Mt. Abu
(D) Kanchenjunga
(B) Matterhorn

Question 30.
The deepest fjord of the world is
(A) Dry galski fjord
(B) Geiranger fjord
(C) Soque fjord
(D) King oscar fjord
(C) Soque fjord

Question 31.
Deep cracks on the surface of the mountain glacier are called
(A) Nunatak
(B) Creavasse
(C) Arete
(D) Cirque
(B) Creavasse

Question 32.
A pyramidical peak formed due to recession and intersection of three or more cirques is called
(A) Horn
(B) Col
(C) Nunatak
(D) Arete
(A) Horn

Question 33.
The higher peaks and mounds surrounded by ice from all sides are called
(A) Arete
(B) Nunatak
(C) Cirque
(D) Hom
(B) Nunatak

Question 34.
Which glacial landform is formed by abrasion and plucking of step faults?
(A) Nunatak
(B) Roche Moutonne
(C) Grag and tail
(D) Glacial stairways
(D) Glacial stairways

Question 35.
The rock debris carried by the glaciers are collectively called
(A) Tills
(B) Avalanches
(C) Glacial drifts
(D) Moraines
(C) Glacial drifts

Question 36.
Which of the following terms refer to the depositional landforms of direct glacial origin?
(A) Moraines
(B) Talus
(C) Rock waste
(D) Regolith
(A) Moraines

Question 37.
Which of the following are depressions in the outwash plains ?
(A) Kettles
(B) Cone Kames
(D) Hummocks
(A) Kettles

Question 38.
A tributary valley associated with the main glacial valley is called a
(A) Hanging valley
(B) V-shaped valley
(C) U-shaped valley
(D) None of these
(A) Hanging valley

Question 39.
An armchain type of hollow cut into the mountain by a moving glacier is called a ______.
(A) U-shaped valley
(B) Roche moutonne
(C) Cirque
(D) Glacier lake
(C) Cirque

Question 40.
Glacial troughs occupied by the sea are called
(A) Fjords
(B) Glacial groones
(C) Finger lakes
(D) None of these
(A) Fjords

Question 41.
Fjord coasts are common in
(A) Norway
(B) Germany
(C) Sweden
(D) France
(A) Norway

Fill in the blanks : 1 Mark

1. Glaciers flow faster in the ________ season.
2. The German word ‘berg’ means _______.
3. Bergschrunds are known as _______ in French.
4. The rock fragments of different sizes coming down by the melting of the glaciers is called _______.
5. The longest glacier of India is _______.
6. The Peterman glacier of greenland is a _______ glacier.
7. The ice line or snow line lies at the highest altitude in the _________ region.
8. The largest continental glacier of the word is the ______ glacier.
9. ________ is known as the land of fjords.
10. Corrie lakes are known as ______ in France.
11. The snow-less peaks in an ice covered regions are called _______.
12. Drumlins looks like _______.
13. The limit below which snow starts melting is called _______.
14. Eskar is a ________ landform formed by glacier.
15. Horizontal and parallel cracks or fractures found on the surface of a glacier are called _______.
1. Summer
2. mountain
3. Rimaye
4. Boulder clay
5. Siachen
6. Continental
7. Equatorial
8. Lambort
9. Norway
10. Cirques
11. Nunatakes
12. inverted boats
13. snowline
14. Depositional
15. Crevasse

State True or False : 1 Mark

1. The period between two ice ages is called the non-ice age. [ ]
2. The outwash plain separated by a river is called the valley train. [ ]
3. Presently, the largest number of glaciers are found in Asia. [ ]
4. Eskers are formed by erosional work of glaciers. [ ]
5. Glaciers do not lie at the same altitude always. [ ]
6. The glacial valleys are U-shaped. [ ]
7. The floating blocks of ice in oceans are called snow lines. [ ]
8. The tongue-shaped part in front of a moving glacier is called a shout. [ ]
9. Matterhorn peak in the Alps is a pyramidical peak. [ ]
10. Small continental glaciers are known as glacier sheets. [ ]
11. Nunatakes are seen in polar region. [ ]
12. The submerged glacial valleys formed due to erosion by continental or mountain glaciers are called fjords. [ ]
13. The regions clustered with drumlines is also called ‘basket of eggs topagraphy’. [ ]
14. Waterfalls are formed from the meltwater of hanging valleys after deglaciation. [ ]
15. Altitude of snowline varies with latitudes. [ ]
1. True
2. True
3. False
4. False
5. True
6. True
7. False
8. True
9. True
10. False
11. True
12. True
13. True
14. True
15. True

Answer in few words : 1 Mark

Question 1.
What is a crevasse?
Cracks that develop on the surface of a glacier.

Question 2.
What is snow line?
The altitude above which there is permanent snow lying throughout the year is known as the snow line.

Question 3.
What is a glacier?
A glacier is a body of ice that flows downwards along the slope of the land due to gravity.

Question 4.
What is a snout ?
The glacier’s downstream end is called snout.

Question 5.
What is iceberg ?
Huge blocks of ice that break off from glaciers and fall into the sea are called icebergs.

Question 6.
Where do piedmont glaciers lie ?
At the foot of the mountains.

Question 7.
Which is the world’s longest continental glacier ?
Lambert glacier in Antarctica.

Question 8.
What are the main works of a glacier?
Erosion, transportation and deposition.

Question 9.
How are moraines formed ?
By glacial deposition.

Question 10.
What are kames?
Rounded hillocks of sand and gravel formed due to glacial deposition.

Question 11.
How does a landform comprising of several drumlins look like?

Question 12.
What kind of a glacier is Siachen in India ?
Mountain or valley glacier.

Question 13.
What are compaction of granular snow called ?
Firm.

Question 14.
Which continent has the maximum number of glaciers ?
Antarctica.

Question 15.
Name the largest valley glacier of the world ?
Lambert.

## WBBSE Class 10 Geography Solutions Chapter 1.2 Works of a River

Detailed explanations in West Bengal Board Class 10 Geography Book Solutions Chapter 1.2 Works of a River offer valuable context and analysis.

## WBBSE Class 10 Geography Chapter 1.2 Question Answer – Works of a River

Answer in short : 2 Marks

Question 1.
What is the hydrological cycle?
Water is present on the surface of the earth in rivers, lakes, oceans, ponds and other water bodies. This water gets evaporated by the sun’s heat and mixes with the atmosphere. Again, this vapour condenses and forms clouds and comes back to the earth’s surface as rain or snow. This cyclical movement of water from the earth’s surface and sub-surface to the atmosphere and vice versa is known as the hydrological cycle.

Question 2.
What is tributaries and distributeries ? Give example.
Tributary : A tributary is a stream or a river which flows into a larger river. A tributary does not flow directly into a sea or ocean. For example, river Gomati and Son are tributaries of river Ganga.
Distributary : A stream that flows into a main-stream (or parent) river called distributary. For example, Hooghly is the distributary of Ganga.

Question 3.
What is peneplain?
A more or less level land surface produced by erosion over a long period of time is called peneplain. It is a representation of a near-final stage of fluvial erosion. e.g.-Chotonagpur region.

Question 4.
What is Knick point ?
Knick point refers to a particular point of the surface. where there is a sharp change in the slope of a river. After rejuvination, this particular point of sharp change of river slope occured, which is known as knick point.

Question 5.
What do you mean by rejuvination?
The action of restoring a river or stream to a condition characteristic of a younger landscape is called rejuvination. Rejuvination occured for various reasons, i.e. earthquake, river captured etc.

Question 6.
What is a river ?
A river is a flowing water body, which collects its water from rain and snow melt, flows down the hilly slopes through a natural channel due to gravitational force and meet with any other water body like ocean, sea, lake etc.

Question 7.
What is a river basin ?
The area drained by the main river, the tributaries and distributaries from the source to the mouth is called the river basin.

Question 8.
What is a water-divide?

The highland that separates two or more river basins lying adjacent to each other is called a water-divide. Usually the hills, mountains, ridges etc. act as waterdivides.

Question 9.
What is a river valley ?

The channel through which a river flows, is known as the river valley. The shape and size of the river valley depends on the amount of water, depth of water and speed of the river.

Question 10.
What is an ideal river?
An ideal river is one which has three prominent courses from source to mouth, i.e.- upper course or youth stage, middle course or maturity stage and lower course or old age stage.

Question 11.
Why is river Ganga known as an ideal river ?
River Ganga is known as an ideal river because it exhibits all the three stages of a river. (i) The upper course lies from Gomukh to Haridwar, (ii) The middle course lies from Haridwar to Dhulian in West Bengal, (iii) The lower course lies from Dhulian to Gangasagar in West Bengal.

Question 12.
What is ‘Sixth power law’?
The transportation capacity of a river depends on the river’s velocity and volume of water. If the velocity of the river is doubled, the transportation capacity is increased by 26 = 64 times. This is known as the ‘Sixth power law’ of a river.

Question 13.
Name the methods by which a river erodes.
A river erodes by the methods of – hydraulic action, corrosion or abrasion, attrition and solution.

Question 14.
Name the methods by which a river transports the eroded material.
A river transports the eroded materials by – traction, saltation, suspension and solution processes.

Question 15.
Mention the factors on which the transportation capacity of a river depends.
The transportation capacity of a river depends on – slope of the river valley, velocity of the river, volume of water, size, shape and characteristics of the loadbeing carried.

Question 16.
What is a pot hole ?

The round pot-like holes cut on the river beds by the swirling water and the rock fragments by the process of corrosion or abrasion are called potholes.

Question 17.
What is a plunge pool ?
The depression or hole created at the foot of a waterfall due to falling of water along with rock fragments with high velocity, is known as a plunge pool.

Question 18.
What is a cataract?
When a series of waterfalls come down in steps over a staircase-like land form, it is known as a cataract.

Question 19.
A series of small waterfalls of the same river lying close to each other is called a cascade.

Question 20.
What is a rapid ?
When small streams or waterfalls come down with high velocity by jumping step by step over the area, it is called a rapid.

Question 21.
Name the different types of deltas.
The different types of deltas are : Bird’s foot delta, Arcuate delta and Cuspate delta.

Question 22.
Give a brief introduction of the New Moore island.
The newly formed island at the Indo-Bangladesh border, five kmsouth from the mouth of River Hariyabhanga in the Bay of Bengal, is known as the “New Moore’ or ‘Purbasha’ island.

Question 23.
What is a catchment area or catchment basin ?
In the hilly regions, numerous small streams and springs of water flow from different directions and contribute the water to form a main river. These numerous thin streams and springs help to keep the supply of water continuously for the main river. This region, from the main river takes shape of a basin is called the catchment area or catchment basin.

Question 24.
What do you mea by ‘River regime’ ?
According to F. J. Monkhouse, river regime refers to the seasonal variation of water volume in the river.

Question 25.
Mention the works done by a river in its course of flow.
An ideal river has three stages in its course of flow. In the upper course, the river mainly erodes materials. In the middle course, the main work is transportation of the eroded load. In the lower course, the main work is deposition of the load transported so far.

Question 26.
What is ‘Cusec’ and ‘Cumec’?
‘Cusec’ and ‘Cumec’ are units of measuring the volume of water flowing through a river. ‘Cusec’ refers to the amount of cubic feet of water flowing through a particular point of the river in one second time. ‘Cumec’ refers to the amount of cubic metres of water flowing through a particular point of the river in one second time.

Question 27.
What do you mean by the last limit of erosion of a river ?
Last limit of erosion of a river refers to the last limit of the lower course of the river where its erosive power finally ends. Usually, the sea level is considered as the last limit of erosion of a river.

Question 28.
What do you mean by degradation by river ?
In a river, if the load is lesser than the capacity of load that it can carry, it continues its work of erosion, thus lowering the river beds and widening the walls. This is known as degradation by river.

Question 29.
What do you mean by aggradation by river ?
In a river, if the load is far more than the capacity of load that it can carry, it starts depositing the load, thus increasing the height of landforms and decreasing the depth of the river beds. This is known as the aggradation of river.

Question 30.
Name some important water-divides in India.
The important water-divides present in India are :

1. The Himalayan range (the largest water-divide of India)
2. The Western Ghats (the second largest water-divide of India)
3. The Vindhya and Mahakal ranges (the third largest water-divide of India)
4. The Satpura range.

Question 31.
What is a ‘Fall line’?
In a hilly region or a plateau region, when numerous small rivers flow towards a steep and almost vertical edge of a mountain ridge or plateau, a number of waterfalls are created in a line. This is known as a ‘Fall line’. Eg. – In North America, the Appalacian mountains meet the coastal plains in a steep slope, creating a series of waterfalls along the edge of the range.

Question 32.
Name the landforms created in the upper course of a river.
The different landforms created in the upper course of a river are – V-shaped valleys, U-shaped valleys, gorges, canyons, waterfalls, plunge pools, pot holes, interlocking spurs etc.

Question 33.
Name the landforms created by deposition of rivers.
The different landforms created in the lower course of a river are – alluvial cone, alluvial fan, flood plain, natural levee, meanders, sandbars, delta etc.

Question 34.
What is an arcuate delta?
The deltas whose outer boundary lies in an arch or looks bow-shaped towards the sea are called arcuate deltas. Eg.- deltas of rivers Ganga, Nile, Hwang Ho etc.

Question 35.
What is a bird’s foot delta ?

The deltas that look like a bird’s claws or fingers spreading one beside the other, are called Bird’s foot deltas. Eg. delta of river Mississippi in North America.

Question 36.
is a cuspate delta ?

The deltas which have sharp edges towards the sea, and look like cusps or pointed teeth pointing towards the sea at the edge, are called cuspate deltas. Eg-deltas of rivers Tiber in Italy and Ebro in Spain.

Answer in brief : 3 Marks

Question 1.
When does a river start depositing its load ?
The river starts depositing its load under the following conditions :
(a) If the volume of water in the river reduces due to less rainfall, drought, dry season or percolation through rock beds,
(b) If the slope of the river valley reduces, it also reduces the speed of the river.
(c) If load of the river increases.
(d) If the river flows through a lake for a certain length.

Question 2.
Differentiate between abrasion and attrition.

 Abrasion Attrition i. The river beds and walls get eroded by action of rock fragments hitting against them. i. The rock fragments carried by the river hit against each other and reduce in size. ii. Rock fragments collide against river beds and walls. ii. Rock fragments collide against each other. iii. This type of erosion is very effective. iii. This type of erosion is less effective. iv. This type of erosion creates pot holes, plunge pools etc. iv. This type of erosion creates sand, silt, clay etc. v. Depth and width of river channels increase. v. Depth of river channel is reduced by certain deposition of silt or sand. vi. Abrasion does not hinder transportation of materials by rivers. vi. Attrition hinders transportation of materials to a certain extent.

Question 3.
Why are V-shaped valleys created in the upper course of rivers?
The causes of formation of V-shaped valleys in the upper course of rivers are:

(a) The rivers have high velocity in the upper course. They cut downwards much more than sidewards. Thus the valleys look like a ‘V’.
(b) Sometimes the ‘I’ shaped valleys may collapse to form ‘V’ shaped valleys.
(c) The hard rocks of the river valley walls are difficult to erode by sidewise pressure of water than downward pressure.

Question 4.
Why is erosion predominant in the upper course of a river?
Erosion is predominant in the upper course of a river as – (a) Steep slope of the region gives high velocity to the river and increases its erosive powers. (b) Volume of water remains high due to snow melt as well as rain water, which makes the river more active.

Question 5.
Differentiate between ‘Gorge’ and ‘Canyon’.

 Gorge Canyon i. Very narrow and deep valley created in hard rock mountainous regions. i. Very narrow and deep valley created in soft rock arid and semiarid mountainous regions. ii. Formed by down cutting of river much more compared to side cutting. ii. Formed by down cutting of perennial rivers in arid regions, where side cutting is prevented due to lack of rainfall. iii. Found in wet high fold mountain regions. iii. Found in dry and arid regions and limestone regions as well. iv. Resembles the alphabet ‘V’. iv. Resembles the alphabet ‘I’ v. Eg. – Royal Gorge of Arkansas, Sampo Gorge of Tibet. v. Eg. – Grand Canyon of the river Colorado, USA is the deepest canyon of the world.

Question 6.
Mention the conditions where a waterfall can be created.
Water of a river falling freely from a certain height in the upper course of the river is called a waterfall. Waterfalls can be created by the following conditions:
(a) Hard and soft rock beds lying alternately horizontal, vertical or diagonal to each other.
(b) If a plateau meets a plain in a steep slope.
(c) Faulting across the river valley.
(d) Hanging valleys created by glacial action.
(e) Knick points created due to rejuvination of rivers.

Question 7.
Differentiate between alluvial cone and alluvial fan.

 Alluvial cone Alluvial fan i. When the river leaves the mountainous region and enters a region of less slope suddenly, it deposits its load like pebbles, sand, rock fragments etc. in the form of a cone. This is called an alluvial cone. i. When water flows over the alluvial cones, the depositions of the cones get spread and looks like a halfcircle. This is known as an alluvial fan. ii. This looks like a cone. ii. This looks like a half-circle or a hand fan. iii. Height of the cone is greater than the alluvial fan. iii. Height of the fan is lower than the alluvial cone. iv. Slope is steep. iv. Slope is gentle.

Question 8.
Discuss briefly the different processes of transportation of load by a river.
A river transports its load by the following processes:
(a) Traction : The heavier and large rock fragments are forced to flow down
along the river water by rolling on the floor of the river channel due to gravity.
(b) Saltation : The fragments of rocks are moved downstream by jumping over the river bed continuously.
(c) Suspension : The fine particles of the river’s load remain suspended in the river due to buoyancy of water while they are carried downstream.
(d) Solution : Soluble particles are dissolved in the river water and moved downstream.

Question 9.
What is a flood plain ?

In the lower course, the speed of the river is much less due to very gentle slope of the land. The river starts depositing its load in the river bed itself, thus reducing its water holding capacity. During the rainy season, when excess water comes into the river, it overflows. Much of silt, sand and clay deposits also overflow with the water and spread over large areas. This process of repeated overflow and spread of silt develops an extensive plain on both sides of the river, known as flood plains.

Question 10.
What is a natural levee?
When silt, clay etc, are deposited at the banks of a river in the middle course every year, the height of the banks are increased compared to the adjacent lands. This looks like a natural dam, and is known as a natural levee. Such features on either side of the river channel helps to increase the depth of the river bed and its water holding capacity.

Question 11.
Differentiate between the Catchment Area and River Basin.

 Catchment Area River Basin i. At the source of a river, numerous small streams and springs of water flow downwards from the surrounding highlands to supply water to the main river. This is known as the catchment area. i. The main region through which the main river, tributaries and distributaries flow is known as the river basin. ii. Main function of the catchment area is to supply water to the main river. ii. Main function of the river basin is to collect water from rainfall and other tributaries and make it flow towards the sea. iii. Catchment area lies only at the source of the river. iii. River basin spreads after the catchment area till the mouth of the river. iv. Catchment area is much smaller compared to the basin of the same river. iv. River basin is many times larger than its own catchment area.

Question 12.
By what processes does the river erode in its course of flow ?
A river erodes in the course of its flow by the following processes :

1. Hydraulic action : This is the process by which the river water itself exerts pressure and friction and causes erosion.
2. Corrosion : In this process the rock fragments and pebbles collide against the walls and floor of the river basin and cause erosion.
3. Attrition : The rock fragments and pebbles flowing in the river collide against each other and break into smaller fragments.
4. Cavitation : In a turbulent stream, numerous air bubbles are created. These bubbles exert severe pressure when they burst, thus can cause erosion.
5. Solution : Soluble materials may get dissolved in river water and get removed. This causes erosion.

Question 13.
On what factors does the transportation capacity of a river depend ?
The transportation capacity of a river depends on the following factors :

1. Slope of land: Greater the slope of land, greater will be the velocity of the river, hence, greater will be the capacity of transportation.
2. Amount of water : Greater the amount of water, greater is the transporting capacity of a river.
3. Amount of load : Greater the amount of load, lesser is the transportation capacity.
4. Size and weight of load: Greater the size and weight of load, lesser is the transportation capacity.

Question 14.
On what factors does the erosive power of rivers depend?
The erosive power of the rivers depend on the following factors :

1. Speed of the river: The speed of the river depends on the slope of the land. Higher the speed, greater the erosive capacity of the river.
2. Amount of water : Greater the amount of water present in a river, greater is its erosive power. It can be noted that in rainy seasons, when the water level of the rivers increases, their erosive powers also increase.
3. Nature of rocks in river bed : If the rocks of the river bed are soft in nature, the river will erode more. If the rocks are hard, erosion will be less.
4. River load: The amount of load carried by the river also influences erosive power of the river. Greater the amount of load, greater is the amount of erosion.

Question 15.
How are pot holes formed ?

The river bed is much eroded by the rock fragments and pebbles being carried by the river itself. When these rock fragments hit constantly against the river bed, the softer rocks get eroded away, creating hollows or depressions. When water falls into these depressions, they swirl around and then move forward. These shallow depressions or hollows are called pot holes.

Question 16.
What is a meander?

In the course of flow of a river, the speed of the river is much reduced from the middle course towards the lower course. This reduces the carrying capacity of the river. The river starts depositing materials within its own bed as well as the banks. Thus obstructions are created in the course of flow. To avoid these obstructions, the river starts taking curves gradually and elongates its course, so that all can be accommodated. These curved portions of the river are called meanders. Meanders may get intensely curved and cut off to form ox-bow lakes.

Question 17.
What is an ox-bow lake?

In the middle and lower course of a river, the speed of the river reduces so much that the carrying capacity of the river also reduces. It starts depositing materials within its own bed as well as on the banks. Thus, the river starts taking curves, forming meanders. When these meanders take intense curves, they may get cut off from the main river due to depositions that block their way. The main river flows by in a straight path and the cut-off part remains stagnant, forming a lake. These lakes look like the foot of a horse or an ox. Hence, they are called ox-bow lakes.

Question 18.
What do you mean by river capture?
When two streams are flow along a water divide, the stronger stream erodes faster and greater with the passage of time, the headward erosion of the stronger stream erode the water divider and flows instead down the bed of neighbouring weaker stream. This phenomena is called river capture. This can happen for several reasons, including earth movement, landslide or ice sheet sliding etc.

Question 19.
Classify deltas according to their origin and explain them.
There are two types of deltas according to their origin, such as (A) Constructive and (B) Destructive deltas.
(A) Constructive delta : Rivers deposited all eroded materials (sand, silt etc) into its beds in the lower course and form triangled new land called delta. These deltas are also called constructive delta. Such as Majuli.
(B) Destructive delta : When these deltas are continuously changing their shape and size for the action of waves, and tides, they are called desctructive delta. Such as deltas of river Rhone

Question 20.
Why do floods occure frequently in the lower course of the river?
Lower course of the rivers are prone to frequent floods. The reasons behind this are :
i. Surface slope is almost zero in the lower course of the river. So huge amount of water of the river can not able to flow with high velocity towards the sea.
ii. River beds are loaded with maximum deposits. Thus the depth of the river channel gradually decreases. During the rainy season, as the extra amount of water is added to the river, both the banks of the river get flooded.

Answer in details : 5 Marks

Question 1.
Describe the landforms created by erosion of river in the upper course.
The various landforms formed in the upper course of the river are :

(a) Gorge or V-shaped valley : In the upper course, the down cutting force of the river is much more than lateral erosion. Hence, the channel develops more depth than width, and looks like a ‘V ‘ shaped valley.
(b) Canyan or I-shaped valley : When the river flows through an arid region made up of non-resistant rocks, most of its energy is spent in down-cutting rather than widening of the valley. Thus the valley developed looks like ‘I’ shaped.
(c) Pot holes : Round disc-like depressions curved by the swirling water and rock fragments on the bed or floor of the river are called pot holes.

(d) Waterfalls : When water of the river falls freely from a height due to very steep slope, it is called a waterfall. They are further classified into rapids, cataracts and cascades.

(e) Interlocking spurs : When a number of projecting ridges or spurs extend from opposite sides of the wall of a V-shaped valley alternately, they seem to overlap or interlock. Such a series of spurs are called interlocking spurs.

Question 2.
Discuss the landforms formed due to deposition in the middle course of a river.

The landforms formed in the middle course of a river are :
(a) Alluvial cone : As the river descends from a mountain and enters into a plain, it deposits extra load at the foothills in the form of a cone. This is known as alluvial cone.
(b) Alluvial fan : When the alluvial cone spreads wider and looks like a half-wide or a hand fan, it is known as the alluvial fan.
(c) Flood plains : Flooding of the rivers spread silt and clay to extensive areas on both sides of the river channel. This forms the flood plains.

(d) Natural levee : Repeated flooding tends to increase the height of the river banks and looks like long extensive dams along the banks. This is called natural levee.
(e) Meanders : The river develops broad bends and ‘S’ curves while flowing through the depositions in the middle course. These are called meanders.

(f) Ox-bow lakes: When the curves of the meander comes too close, the loop tends to join, forming a neck. The curved portion of the loop is gradually cut-off by further deposition. This horse-shoe shaped stagnant water body is known as the ox-bow lake.

Question 3.
What is a delta ? Why do deltas develop at the mouth of the rivers?
Velocity of the river is almost nil where it meets with the sea. Thus, the heaviest amount of depositions occur here. The main channel is broken into numerous distributaries as more and more depositions take place. The region acquires a triangular shape and looks like the Greek letter Delta (Δ), hence the name. Deltas develop under the following conditions :

(a) The sea bed near the mouth of the river is very shallow.
(b) Slope is negligible.
(c) Tidal action is low.
(d) Huge amount of bed load.
(e) Numerous tributaries of the main river to add up to the load.
(f) Low current of river water at the mouth.
(g) Wind blowing in opposite direction to the flow of river water.
(h) Enclosed sea with lesser disturbances.
(i) Long course of the river.
(j) Absence of lakes and other depressions in the path of the river.
(k) Wet and humid weather rather than dry weather.

Question 4.
Compare and contrast alluvial cone with delta.

 Alluvial cone Delta i. Formed due to deposition of materials at the foot hills of mountains when the river enters the plains from the mountains. i. Formed due to heavy deposition of materials when the river tends to meet the sea at the lower course. ii. Formed of coarse and bigger rock fragments deposited at the foot hills. ii. Formed of very fine silt and clay particles deposited at the mouth of the river. iii. Resembles a cone. iii. Resembles a flat triangle area. iv. Covers a smaller area. iv. Covers a larger area. v. No other classification. v. Can be classified into bird’s foot, arcuate and cuspate deltas.

Multiple Choice Questions (MCQ) : 1 Mark

Question 1.
A river is a part of the – cycle.
(A) Hydrological
(B) Biological
(C) Ecological
(D) Atmosphere
(A) Hydrological

Question 2.
The river attains water from
(A) Rainfall
(B) Snow melt
(C) Rain and show melt
(D) None of these
(C) Rain and show melt

Question 3.
Qarrying and removing of loose bedrocks by running water of a river is known as
(A) Corrosion
(B) Hydraulic action
(C) Solution
(D) Attrition
(B) Hydraulic action

Question 4.
The process of erosion by collision between flowing rocks and the river bed and walls is called
(A) Corrosion
(B) Traction
(C) Solution
(D) Attrition
(A) Corrosion

Question 5.
Erosion of materials by dissolving in river water is called
(A) Abrasion
(B) Attrition
(C) Solution
(D) Saltation
(C) Solution

Question 6.
Wearing down of rock materials by collision against each other is known as
(A) Attrition
(B) Solution
(C) Transportation
(D) Saltation
(A) Attrition

Question 7.
Large rocks and pebbles are dragged by the river by the process of
(A) Transportation
(B) Traction
(C) Saltation
(D) Solution
(B) Traction

Question 8.
Rock fragments move downstream by jumping continuously by the process of
(A) Siltation
(B) Saltation
(C) Solution
(D) Attrition
(B) Saltation

Question 9.
Rock fragments remain suspended and are flown down by
(A) Solution
(B) Suspension
(C) Siltation
(D) Saltation
(B) Suspension

Question 10.
Soluble particles are carried away by
(A) Saltation
(B) Corrosion
(C) Suspension
(D) Solution
(B) Corrosion

Question 11.
The beginning of a river is called the
(A) Channel
(B) Silt
(C) Course
(D) Source
(D) Source

Question 12.
The path of the river is called the
(A) Channel
(B) Bed
(C) Source
(D) Mouth
(A) Channel

Question 13.
Small rivers joining the main river are called
(A) Tributaries
(B) Distributaries
(C) Source
(D) Mouth
(A) Tributaries

Question 14.
Small streams that flow out of the main river are called
(A) Tributaries
(B) Source
(C) Distributaries
(D) Mouth
(C) Distributaries

Question 15.
Two rivers meet at the –
(A) Mouth
(B) Source
(C) Confluence
(D) Channel
(C) Confluence

Question 16.
A landform of the upper course of the river is
(A) Alluvial cone
(B) Canyon
(C) Meander
(D) Ox-bow lake
(B) Canyon

Question 17.
Pot hole is created in the course of river.
(A) Lower
(B) Middle
(C) Upper
(D) Everywhere
(C) Upper

Question 18.
Natural levee are formed in course of river.
(A) Upper
(B) Lower
(C) Middle
(D) Everywhere
(C) Middle

Question 19.
Sand bars and deltas are formed in cource of river.
(A) Upper
(B) Lower
(C) Middle
(D) Everywhere
(B) Lower

Question 20.
Materials deposited by rivers are called
(A) Moraine
(B) Debris
(C) Salts
(D) Alluvium
(D) Alluvium

Question 21.
How much of the landform formation is influenced by the work of rivers?
(A) 30 %
(B) 50 %
(C) 60 %
(D) 70 %
(D) 70 %

Question 22.
Who named the landform ‘delta’ for the first time?
(A) Herodotus
(B) Pithagoras
(C) Thornbury
(D) Davis
(A) Herodotus

Question 23.
Which instrument is used to measure the water current of a river ?
(A) Barometer
(B) Altimeter
(C) Currentmeter
(D) Rain gauge
(C) Currentmeter

Question 24.
An example of a water divide in India is
(A) Western ghats
(B) Punjab plains
(C) Eastern coastal plains
(D) Ganga plains
(A) Western ghats

Question 25.
The delta of river – looks like the teeth of a saw.
(A) Nile
(B) Tiber
(C) Ganga
(D) Mississippi
(B) Tiber

Question 26.
A bird’s foot delta is seen in the river
(A) Mississippi
(B) Ganga
(C) Nile
(D) Rhine
(A) Mississippi

Question 27.
Potholes are created in the river channels due to
(A) Friction
(B) Abrasion
(C) Action of bubbles
(D) None of these
(B) Abrasion

Question 28.
Canyons are created due to
(A) Erosion
(C) Deposition of rivers.
(B) Transportation
(D) Transportation and deposition
(A) Erosion

Question 29.
The Majuli island is located in the river
(A) Ganga
(B) Brahmaputra
(C) Indus
(B) Brahmaputra

Question 30.
The depressions created at the base of waterfalls are called –
(A) Potholes
(B) Plunge pools
(C) Alluvial fans
(D) Oxbow lakes
(B) Plunge pools

Question 31.
The largest river basin of the world is
(A) Nile basin
(B) Ganga basin
(C) Amazon basin
(D) Rhine basin
(C) Amazon basin

Question 32.
The water flowing through a river channel is measured in
(A) Knots
(B) Cm
(C) Cusec
(D) Inch
(C) Cusec

Question 33.
The erosional work of the rivers depends on
(C) Velocity
(D) All of the above
(D) All of the above

Question 34.
Which of the following involves removal of loosened materials of the rocks of valley walls and valley floors with the help of erosional tools?
(A) Solution
(B) Abrasion or Corrasion
(C) Attrition
(D) Traction
(B) Abrasion or Corrasion

Question 35.
Which of the following is the mechanical tear and wear of the erosional tools in themselves?
(A) Traction
(B) Corrosion
(C) Abrasion
(D) Attrition
(D) Attrition

Question 36.
The level at which a river completely stops erosional work is called
(A) Base level
(B) End level
(C) Maximum level
(D) Local level
(A) Base level

Question 37.
A very deep and narrow valley is called a
(A) Gorge
(B) Canyon
(C) Pothole
(D) Plunge pool
(B) Canyon

Question 38.
Which of the following may be defined as a vertical drop of water of enormous volume from a great height in the long profile of the river?
(A) Terraces
(B) Rapids
(C) Cataracts
(D) Waterfalls
(B) Rapids

Question 39.
Alternate bands of hard and soft rocks give birth to a series of small step-like falls called
(A) Cataracts
(B) Rapids
(D) Terracas

Question 40.
Which of the following refers to the bends in the longitudinal courses of the rivers?
(A) Waterfalls
(B) River terraces
(C) River meanders
(D) River valleys
(C) River meanders

Question 41.
Which of the following is the result of both erosion and deposition?
(A) River valley
(B) River terraces
(C) Plunge pool
(D) Meanders
(D) Meanders

Question 42.
The depositional features at the foot hills of the Himalayas are called
(A) Bhangar
(B) Bhabar
(D) None of these
(B) Bhabar

Question 43.
Which of the deltas are formed when the river water is as dense as the sea water?
(A) Birdfoot delta
(B) Estuarine delta
(C) Arcuate delta
(D) Truncated delta
(C) Arcuate delta

Question 44.
Ganga delta is an example of
(A) Arcuate delta
(B) Birdfoot delta
(C) Estuarine delta
(D) Truncated delta
(A) Arcuate delta

Question 45.
Grand Canyon in United States is the work of river
(B) Mississippi
(C) Tennessee
(D) Missouri

Question 46.
The longest river of the world is :
(A) Mississippi-Missouri
(B) Nile
(C) Ganga
(D) Amazon
(B) Nile

Question 47.
‘Kuick point’ of a river is seen is
(A) Ox-bow
(B) Flood plain
(C) Waterfall
(D) Pot holes
(C) Waterfall

Question 48.
Alluvial cones are formed in the rivers
(A) Upper
(B) Middle
(C) Lower course
(D) None
(B) Middle

Question 49.
The river valley created in the dry regions due to deepcutting of soft rocks are called
(A) Gorge
(B) Canyon
(C) Hanging valley
(D) Creavasses
(A) Gorge

Question 50.
The very deep and narrow ‘v’ shaped valley are called
(A) Gorge
(B) Canyon
(C) Interlocking Spur
(D) Waterfalls
(B) Canyon

Question 51.
The unit for measuring the volume of water flowing through a certain part of a river is said to be 1 cusec, when the volume of water flowing through is
(A) 1 cubic meter
(B) 1 cubic feet
(C) 1 cubic inch
(D) 1 cubic centimeter
(D) 1 cubic centimeter

Question 52.
When the speed of the river increase by two times, its carrying capacity increased by
(A) 7
(B) 2
(C) 3
(D) 64 times
(D) 64 times

Question 53.
The main cause of submergence of the island of sundarbans is
(A) Heavy rainfall
(B) Cyclone
(C) Rise in sea level
(D) Flood
(C) Rise in sea level

Question 54.
The sediments depositions on the convex side of meanders are called
(A) Pool
(B) Point bar
(C) Pluge pool
(D) flood plain.
(B) Point bar

Question 55.
A falline is a
(A) Band of hard rocks
(B) Chain of waterfalls
(C) Steepness of valley side
(D) All of these
(B) Chain of waterfalls

Fill in the blanks : 1 Mark

1. V-shaped river valleys are found in the ________ stage of the river.
2. The formation of rapids and waterfalls is found in the _______ course of the river.
3. The delta in Inda is the largest delta of the world.
4. The breaks in the channel gradient caused by rejuismation of rivers are called ________.
5. The average height of natural levees is ________.
6. If the speed of the river is doubled, its carrying capacity increases by _______ times.
7. The gersoppa waterfalls are also known as ________.
8. The _______ delta of India is an active delta.
9. River _______ is known as the sorrow of Bengal.
10. The waterfalls move _______ of the river.
11. The narrow plain region between two rivers is called the ________.
12. The landform which separates two river systems is called the ________.
13. _______ lakes are created near delta regions.
14. Deltas are created in the _______ course of rivers.
15. Alluvial fans are created at the _______ of mountains.
16. River _______ is an inland river of India.
17. The New Moore island is known as _______ in Bangladesh.
18. A fault lying across the river in a mountanious region gives rise to ________.
19. In the upper course of a river, downcutting of valleys mainly occure due to ________.
20. The longest river of the world is river _______.
21. The island of Newmoore and Ghoramara have submerged due to ________.
22. The river erodes least in the _______ course.
23. The term meander came from the river ________.
24. Holes formed by abrason on river bed are called _______.
25. According to the name of _______ river, the zigzag course of a river is as meander.
Amswer:
1. Youthful
2. Upper/Youthful
3. Ganga-Brahmaputra
4. Knick points
5. 10 m
6. 64
7. Jog falls
8. Sundarban
9. Damodar
11. Doab
12. Water divide
13. Oxbow
14. Lower
15. Foothill
16. Luni
17. South Talpatti
18. Waterfalls
19. Abreasion
20. Nile
21. Rise in the sea level
22. Lower
24. Pot holes
25. Meanders.

State True or False : 1 Mark

1. Interlocking spurs are found in the lower course of the rivers. [ ]
2. If slope of land increases, the speed of river reduces. [ ]
3. No delta has developed at the mouth of river Narmada. [ ]
4. River Godavari is an ideal river. [ ]
5. River Brahmaputra is the longest river of India. [ ]
6. The river Ganga rises from the Chemuyung Dung glacier. [ ]
7. The New Moore is a newly formed island of the Sundarbans. [ ]
8. The process of friction of rock fragments with the river bed is called abrasion. [ ]
9. The middle course of the river Ganga lies between Allahabad and Patna. [ ]
10. Canyans are formed in cold climatic regions. [ ]
11. The rivers mostly erode sidewards in the upper course. [ ]
12. Meanders are created when the speed of the river increases. [ ]
13. River Ganga is a perenial river. [ ]
14. The mouths of the rivers are generally wide. [ ]
15. Deep creeks and estuaries are found in the Sundarban regions. [ ]
16. The plains formed at the base level of erosion by rivers has been termed peneplains by Davis. [ ]
17. The Dasam falls have been formed in the river Subarnarekha [ ]
18. ‘Meander’ comes from the river Menderes in Turkey. [ ]
19. The largest river island of the world is Ilha-da-Marajo. [ ]
20. The hairpin bend of a river is also called the ‘elbow of river capture’. [ ]
21. The main work of the river in its mountaneous course is erosion. [ ]
22. Work of river starts above the snowline. [ ]
23. Potholes are created in the riverbeds due to abrasion and attrition. [ ]
24. The sea level is the last limit of erosion. [ ]
25. The Grand Canyon lies in the course of river Colorado. [ ]
26. The scientific study of the river is known as potamology. [ ]
27. Rapids are larger than cascade in dimension. [ ]
28. Waterfalls are mostly formed at the upper stages of the rivers. [ ]
29. Oxbow lakes are seen in the upper course of a river. [ ]
30. Canyons are ‘U’ shaped valley. [ ]
31. Pot holes are formed at the base of waterfall. [ ]
32. The confluence of Alakananda and Bhagirathi rivers is at Devprayag. [ ]
1. False
2. False
3. True
4. False
5. False
6. False
7. True
8. True
9. True
10. False
11. False
12. False
13. True
14. True
15 . True
16 . True
17. True
18. True
19. False
20. True
21. True
22. True
23. True
24. True
25. True
26. True
27. False
28. True
29. False
30. False
31. False
32. True

Match the following :

 List 1 List 2 A. Arcuate delta 1. Mississippi delta B. Birdfoot delta 2. Yellow river delta C. Esturanine delta 3. Nile delta D. Abandoned delta 4. Hudson delta

codes:

[D]

Answer in few words : 1 Mark

Question 1.
What is a river?
A large stream of flowing water along the slope on the earth’s surface.

Question 2.
What are the main works of a river?
Erosion, Transportation, Deposition.

Question 3.
How many courses does an ideal river have ?
Three courses – upper, middle, lower.

Question 4.
Where does a river start and end ?
The river starts at the source and ends at the mouth.

Question 5.
What is a river basin ?
The area drained by the main river, tributaries and distributaries.

Question 6.
Name some landforms of the upper course of the river.
V-shaped and I-shaped valleys, gorges, canyons, pot holes, waterfalls etc.

Question 7.
Name some landforms of the middle course of the river.
Alluvial cones and fans, flood plains, natural levee, meanders, ox-bow lakes etc.

Question 8.
Name some landforms of the lower course of the river.
Sand bar, delta, braided channel etc.

Question 9.
Which is the largest delta of the world ?
The Ganga-Brahmaputra delta.

Question 10.
Where was the Lohachara island situated ?
Sundarban.

Question 11.
How far does the upper course of river Ganga lie?
Gomukh to Haridwar.

Question 12.
On which course of the river depositional activities are the least?
Upper course.

Question 13.
What is the curved of a river is called ?
Meandar.

Question 14.
Name the place where the river meets the sea.
Estuary.

Question 15.
What is the sediment carried by the river called ?

Question 16.
Name the process of erosion in which air bubbles trapped in small spaces implode to erode rocks.
Cavitation.

Question 17.
Which is the longest estuary of the world ?
Gulf of Ob.

## WBBSE Class 10 Geography Solutions Chapter 1.1 Exogenetic Forces

Detailed explanations in West Bengal Board Class 10 Geography Book Solutions Chapter 1.1 Exogenetic Forces offer valuable context and analysis.

## WBBSE Class 10 Geography Chapter 1.1 Question Answer – Exogenetic Forces

Answer in short : 2 Marks

Question 1.
What do you mean by landform ?
Landform refers to the shape, height, ruggedness, slope etc. of the earth’s surface. In a nutshell, landform is the appearance of the surface of the earth. According to W.M. Davis, ‘Landscape’ is the function of structure, process and stage.

Question 2.
What do you mean by landform creating processes ?
The physical and chemical processes that have been working since the birth of the earth to create, change, reform or rebuild a landform are called landform creating processes. In short, the processes that act inside and outside the earth’s surface and lead to formation of various landforms are called landform creating processes.

Question 3.
What are exogenetic processes of landform building ?
The processes of landform creation that derive their force from natural sources like sun, wind, heat, air pressure, humidity, rainfall, river, glacier, sea waves etc. are called exogenetic processes. The main sources of energy of such processes are the sun and the earth’s atmosphere.

Question 4.
What do you mean by base level of erosion ?
A base level of erosion is an imaginary surface of irregular shape, inclined towards the lower end of the principal river or its trunk, under which the stream and its tributories were unable to erode. It can be further divided into ground base level, temporary base level and local base level.

Question 5.
In how many parts can exogenetic forces be divieded ?
Exogenetic forces on landform creation can be divided into two parts – i. Static physical forces : atmospheric heat, pressure, humidity, cloud cover, rainfall, dew frost etc. ii. Dynamic physical forces : river, wind, glacier, mass wasting, sea waves, ocean currents etc.

Question 6.
According to Chamberlen and Salisbury (1904) gradation is a process by which the uneven and rough surface of the earth is gradually smoothened by erosion or deposition in order to attain a plain and polished landform. This is brought about by the exogenetic processes by changing the heights of the different landforms.

Question 7.
Classify the exogenetic processes.

Question 8.
The process by which the height of mountains, hills and plateaus are reduced by erosion and mass removal, which result in lower landforms is known as degradation as a whole. The processes of degradation can be divided into weathering, erosion and mass wasting.

Question 9.
What is weathering ?
Weathering comes from the word ‘weather’. Weathering refers to breaking or fragmentation of rocks by the action of different weather elements like heat, pressure, humidity, cloudiness, rainfall, dew etc. The broken rock fragments lie in situ.

Question 10.
What is erosion?
The process of removal of broken and fragmented rock material by dynamic forces of nature like river, wind, glacier, waves etc. thus reducing the height of the original landform is called erosion.

Question 11.
What is mass wasting ?
In hilly regions, if rain water percolates through the soil or rocky beds, the materials get loosened. These soil and rocky materials may fall down in huge masses along the slope due to gravitational force. Such movement of earth materials in huge masses along slope of land is called mass wasting.

Question 12.
The earth materials brought down by the dynamic forces of nature (river, glacier, wind etc.) due to degradation are deposited in the lower slopes in lowlands, basins or depressions. The process of such accumulation of materials, thus increasing the height of the current landform, is known as aggradation.

Question 13.
Name some landforms formed by degradation.
Landforms created by degradation are : monadnock, inselberg, mesa, butte, dhand of desert region, corrie, corrie lake etc.

Question 14.
Name some landforms formed by aggradation.
Landforms created by aggradation are : loess plains, flood plains, alluvial cones and fans, moraines, drumlin, outwash plains, sand bars, beaches, stalactite, stalagmite etc.

Question 15.
What is the last limit of erosion?
When the exogenetic processes cut and lower an undulating rugged highland to a smooth slope where no more erosion occurs, this is known as the last limit of erosion.

Question 16.
What are the biological processes of landform creation?
The exogenetic processes that cause weathering, transportation, erosion and deposition of earth materials due to interference of biological agents like man, plants and animals are called biological processes of landform creation.

Question 17.
What is denudation?
When the weathered earth materials are removed from their position by erosion and mass wasting, the surface beneath the debris becomes open and forms a new landform. This process of opening up of the new surface of the landform is called denudation.
Denudation = Weathering + erosion + mass wasting.

Question 18.
How can mass wasting be classified?
Mass wasting can be classified into two parts – i. Slow flowing and ii. Fast flowing.

Question 19.
What do you mean by gradational forces?
Landforms are initially formed with the help of geotectonic forces that work from within the earth’s interior. These are further sculptured by the static and dynamic forces that act on the surface of the earth. These forces tend to reduce the landforms to a smooth rolling plain or graded profile. These forces are known as gradational force.

Question 20.
i. Static forces – These are the forces that have no motion, but help in formation or sculpturing of landforms. Eg. – Heat, pressure, humidity, cloudiness, rainfall etc.
ii. Dynamic forces – These are the forces that have motion and help actively in changing landforms. Eg. – rivers, wind, waves, glaciers, ocean currents etc.

Question 21.
How can the degradation processes be classified?
Degradation processes can be classified into – i. weathering ii. erosion iii. mass wasting.

Question 22.
What is the outcome of gradation?
By gradation, the lower regions are filled up and elevated while the higher regions are reduced, so that ultimately a smooth and rolling plain is formed, where neither erosion nor deposition is required.

Question 23.
Why do some geologists refuse to consider weathering as a part of gradational process?
In weathering, rock fragments break off from parent rocks, but they are not removed from position. They lie in dumps where they have been broken from. Thus, height or altitude of the landform is not much reduced, and no gradation is achieved unless the materials are removed. Hence, some geologists refuse to consider weathering as a part of gradational process.

Question 24.
What are biological processes of gradation?
The processes by which plants, animals and man interfere and cause weathering, transport and erosion of rock fragments, deposition of these debris in low lands, thus causing formation of a graded profile are called biological processes of gradation.

Question 25.
Name four exogenetic forces.
The exogenetic forces are- i. River, ii. Wind, iii. glacier iv. Sea waves.

Question 1.
What do you mean by exogenetic processes? Give examples.
The word ‘Exogenetic’ comes from the words ‘Exo’ (meaning outside) and ‘Genesis’ (meaning creation). Hence, ‘exogenetic’ refers to forces that are created outside the earth’s surface. The exogenetic processes are controlled by static natural forces (like sun, pressure, humidity, rainfall etc.) and dynamic natural forces (like river, wind, glacier etc.). These processes work for a long time on the surface of the earth, create new sculptures and gradually change the present landforms.

Question 2.
What are the characteristics of exogenetic processes?
The characteristics of exogenetic processes are :
i. These are slow processes.
ii. They change the current landforms.
iii. They occur by the agents like river, wind, glacier, sea waves, ground water, tides etc.
iv. These are very time consuming processes.
v. By these processes, some landforms are lowered while some landforms gain height.
vi. Landforms are changed into smooth graded profiles.
vii. The sun and the atmosphere are the main sources of energy.
viii. Slope plays an important role.

Question 3.
Describe briefly the exogenetic processes of landform creation.
i. Degradation: The processes which result in lowering the height of high landforms are called degradation processes.
Result : The primary landforms (mountains, hills, plateaus etc.) are transformed into secondary landforms.
Processes: Weathering, mass wasting, erosion.

ii. Aggradation : The processes which result in increasing the height of landforms by filling up of lowlands, basins or depressions are called aggradation processes.
Result : Formation of loess, alluvial cones and fans, flood plains, natural levee, delta, moraines, drumlins, out wash plains etc.

iii. Biological processes: The exogenetic processes that create new landforms with the interference of man, animals and plants are called biological processes.

Question 4.
Compare and contrast between weathering and gradation.

 Topic Weathering Gradation i. Definition Breaking and fragmentation of rocks and lying in situ. Attaining of a smooth profile by erosion, transportation and deposition of earth material. ii. Energy Static sources of energy like heat, pressure humidity, rainfall etc. Both static and dynamic sources of energy like river, wind, glacier, sea waves etc. iii. Source of energy Solar energy and weather elements. Static and dynamic natural sources of energy. iv. Process Mechanical, chemical and biological weathering. Degradation, aggradation and biological process. (v. Nature of process Static process. Both static and dynamic. vi. Movement of materials Rocks are fragmented but are not moved. Rocks are fragmented, eroded or moved and deposited elsewhere. vii. Result Main process of soil formation Process of landscape formation and graded land profile.

Question 5.

 Topic Degradataion Aggradation i. Definition Process of erosion and removal of earth’s material and reducing the height of original landform. Process of deposition of eroded material in lowlands and depressions and increasing the height of original landforms. ii. Process Weathering, erosion and mass wasting. Deposition by dynamic natural forces like river, wind, glacier, sea waves etc. iii. Height Original height of landform reduces. Original height of landform increases. iv. Denudation Denudation occurs and new surface of landform is exposed. Original land surface is covered up due to deposition. v. Landforms Monadnock, inselberg, mesa, butte, dhand, canyon, blow hole etc. Loess, alluvial cones and fans, flood plains, delta, moraines etc.

Question 6.
What is the inter-relationship between weathering, erosion and denudation?
Weathering is the process by which rock materials are broken and fragmented by different weather elements. These fragmented materials lie in situ and are not moved. Erosion is the process by which the broken and fragmented rock materials are removed from one place to another by the dynamic forces of nature like river, wind, glacier, sea waves etc. Weathering and erosion are inter dependent. Unless weathering occurs, erosion cannot start. Unless erosion removes the rock debris, further weathering cannot occur.
Denudation is the process by which the outer cover of the landform is removed and a new surface comes out. This cannot occur unless weathering and erosion occur. Hence all these processes are inter dependent.

Question 7.
Give a brief description of gradation.

The term ‘gradation’ comes from the word ‘grade’. This was first used by G. K. Gilbert in 1876. ‘Gradation’ means ‘to bring in to a common or uniform level land’. The landforms created mainly by the geotectonic forces (mountains, hills, plateaus, plains, etc.) are acted upon by various exogenetic forces (weathering, mass wasting, erosion etc by different agents). These landforms one highered, lowered or smoothened by the process of aggradation or degradation. Thus the forces which help to bring about this action are called gradational forces.

Question 8.

Question 9.
Why is the degradation process called a destructive process ?
The process by which highlands including high mountains, hills, plateaus are lowered by different erosional process of river, wind, glacial, seawaves and also by masswasting, denudation to achieved a equllibrium position is called degradation. The original heights of the surface forms are eroded and lowered down by degradation.So that, the said process is also called a destructive process.

Answer in details : 5 Marks

Question 1.
Discuss briefly about exogenetic processes of landform creation.
[All exogenetic processes have been explained part by part earlier].

Question 2.
Discuss the role of exogenetic processes in creation of landforms.
Landforms created by exogenetic processes are mainly formed by degradation or aggradation.
i. Degradation : By this process, the primary landforms like mountains, hills and plateaus are lowered to form secondary landforms.
Landforms : (a) Degradation starts with formation of regolith on the land surface.
(b) High mountains are reduced to plateaus and finally plains.
(c) Plateaus are dissected and finally reduced to plains.
(d) Slope of land reduces and merges with the sea level.
(e) Landforms created are – gorges, canyon, pot holes, waterfalls, plunge pools, interlocking spurs, gour, zeugen, yardang, ventifact, inselberg etc.
ii. Aggradation : By this process, landforms are created by deposition of eroded materials in low lands and depressions.
Landforms : Flood plains, deltas, loess, outwash plains etc.

Question 3.
Discuss the characteristics of exogenetic processes of landform creation.
i. Nature : Very slow process except for landslide and flood.
ii. Place : Occurs mostly on the land surface and sub-surface of the earth.
iii. Forces : Weathering, erosion, mass wasting agents along with river, wind, sea waves, glaciers, tides etc.
iv. Processes : (a) Weathering, erosion and deposition of materials by river, glacier, wind, sea waves, ground water etc.
(b) Mass wasting due to gravitational force.
(c) Mechanical, chemical and biological weathering.
v. Result : Reduction of original landmass to simple, plain, smooth landform mostly by reducing height and some depositions.

Question 4.
Discuss the processes of landform creation by exogenetic processes.
i. Degradation : The processes which result in lowering the height of high landforms are called degradation processes.
Result : The primary landforms (mountains, hills, plateaus etc.) are transformed into secondary landforms.
Processes : Weathering, mass wasting, erosion.

ii. Aggradation : The processes which result in increasing the height of landforms by filling up of lowlands, basins or depressions are called aggradation processes.
Result : Formation of loess, alluvial cones and fans, flood plains, natural levee, delta, moraines, drumlins, out wash plains etc.

iii. Biological processes : The exogenetic processes that create new landforms with the interference of man, animals and plants are called biological processes.

Question 5.
Discuss the role of aggradation and degradation processes in formation of new landforms.
Landforms created by exogenetic processes are mainly formed by degradation or aggradation.
i. Degradation : By this process, the primary landforms like mountains, hills and plateaus are lowered to form secondary landforms.
Landforms : (a) Degradation starts with formation of regolith on the land surface.
(b) High mountains are reduced to plateaus and finally plains.
(c) Plateaus are dissected and finally reduced to plains.
(d) Slope of land reduces and merges with the sea level.
(e) Landforms created are – gorges, canyon, pot holes, waterfalls, plunge pools, interlocking spurs, gour, zeugen, yardang, ventifact, inselberg etc.
ii. Aggradation : By this process, landforms are created by deposition of eroded materials in low lands and depressions.
Landforms : Flood plains, deltas, loess, outwash plains etc.

Question 6.
Discuss the role of the different agents of gradation in formation of new landforms.
The various agents of gradation work on the existing landforms created on the surface of the earth and bring about changes in relief. The role of the different agents of gradation are discussed below :

i. River : River is the most powerful agent of gradation. It erodes the valleys and basins through the processes of abrasion, attrition, solution and hydraulic action. The various landforms created due to erosion are-gorge, canyon, waterfall, plunge pool, interlocking spurs etc. The landforms created due to deposition of materials are – alluvial cone, alluvial fan, natural levee, delta, sand bar etc.

ii. Wind : Wind is an effective agent of gradation in arid regions. It erodes through the processes of abrasion, attrition, friction etc. Landforms produced due to wind erosion are – dhand, blow out, inselberg, gour, zeugen, yardang, dreikanter, ventifact etc. Landforms created due to deposition by wind are sand dunes, loess, etc.

iii. Glacier : Glaciers erode in cold regions by the processes of abrasion, attrition and plucking. Landforms created by glacial erosion are – corrie or cirque, pyramid peak, hanging valley, roche moutonnee. Glaciers deposit materials after they melt in warmer regions. Landforms created by glacial depositions are moraines, drumlin, esker, kame, outwash plains etc.

iv. Sea waves : Sea waves erode with the force of the waves by the processes of abrasion, attrition, collision, friction etc., creating landforms like sea escarpments, sea caves, blow holes, pillars, stumps, stacks etc. The depositional landforms created by waves are- gulfs, bays, sand bars, spits, tombolos, beaches etc.

v. Ground water : Ground water generally erodes through a very slow process mainly by solution in limestone regions. Landforms thus created are – sink hole, swallow hole, uvala, polje, terrarosa etc. The materials dissolved in the water may get deposited to form features like stalactite, stalagmite, pillars etc.

vi. Mass wasting : In hilly regions, landslides and mass wasting may reduce height of the hills and mountains.

vii. Others : Sudden occurrence of tsunami, flood etc. also contribute to degrade or aggrade a region.

Question 7.
What are the results of degradation of landforms ?
i. Creation of regolith on the earth’s surface, which leads to the formation of soil.
ii. High mountains or hills are eroded and lowered to form plateaus. They can be further lowered to form plains.
iii. Rugged plateaus are first dissected by the numerous rivers flowing through them. Later, they are reduced to plains.
iv. Higher plains are further reduced to form lower plains with lesser undulations and minimum slope.
v. The ruggedness of landforms is smoothened and a uniform slope is formed.

Multiple Choice Questions (MCQ) 1 Mark

Question 1.
Landform building processes can be broadly divided into – parts.
(A) 2
(B) 3
(C) 4
(D) 5
(A) 2

Question 2.
The exogenic processes are
(A) Sudden
(B) Medium fast
(C) Slow
(D) Very slow
(D) Very slow

Question 3.
The term ‘grade’ was first used by-
(A) Thornbury
(B) Morris Davis
(C) Gilbert
(D) Prat
(C) Gilbert

Question 4.
Which of these is an exogenic process?
(A) Earthquake
(B) Vulcanism
(C) Sea waves
(D) None of these
(C) Sea waves

Question 5.
The process of lowering the height of landforms is
(D) None of these

Question 6.
Which of these is an example of aggradation ?
(A) Pot hole
(B) Waterfall
(C) Canyon
(D) Delta
(D) Delta

Question 7.
Which exogenic process results in formation of flood plains ?
(D) Biological weathering

Question 8.
What happens to the slope of land due to aggradation ?
(A) Remains same
(B) Becomes nil
(C) Reduces
(D) Increases
(C) Reduces

Question 9.
(A) Erosion
(B) Weathering
(D) Mass wasting

Question 10.
What happens to the slope of land due to degradation ?
(A) Reduces
(B) Increases
(C) Remains static
(D) Becomes zero
(A) Reduces

Question 11.
Which one is not a process of degradation?
(A) River erosion
(B) River deposition
(C) Weathering
(D) Mass wasting
(B) River deposition

Question 12.
An agent of exogenic process is
(A) Earthquake
(B) Vulcanism
(C) Earth movement
(D) River
(D) River

Question 13.
Height of landforms is increased by
(C) Weathering
(D) Lands Lide

Question 14.
Exogenic processes mainly result in –
(D) None of these

Question 15.
The process that creates a balance between erosion, transportation and deposition is –
(A) Weathering
(B) Mass wasting
(C) Atmospheric process

Question 16.
(A) Erosion
(B) Deposition
(C) Weathering
(D) All of these
(D) All of these

Question 17.
A landform created by agradation is –
(A) Fault
(B) Exfoliation
(C) Loess
(D) Mass wasting
(C) Loess

Question 18.
The process of increasing height of a landmass is-
(C) Continental movements
(D) Orogenic movements

Question 19.
Geologists Chamberlen and Salisbury (1904) have remarked exogenic processes as –
(A) Erosion process
(B) Abrasion process
(C) Biological process

Question 20.
Heat, air pressure, humidity, river, wind, glacier etc. are agents of –
(A) Endogenic processes
(B) Non-earth processes
(C) Convectional processes
(D) Exogenic processes
(D) Exogenic processes

Question 21.
(A) Atmospheric
(B) Endogenic
(C) Exogenic
(D) Spacial
(C) Exogenic

Question 22.
Alluvial plains are created by –
Weathering

Question 23.
The work of exogenic processes is –
(A) Constructive
(B) Destructive
(C) Both constructive and destructive
(D) None of these
(C) Both constructive and destructive

Question 24.
Source of energy of all exogenic processes is –
(A) Sun
(B) Space
(C) Earth’s magnetic field
(D) Endogenic forces
(A) Sun

Question 25.
An important exogenic process is –
(A) Tension
(B) Compression
(C) Expansion
(D) Erosion
(D) Erosion

Question 26.
Exogenic processes depend on – forces.
(A) Earth’s interior
(B) Forces working on earth’s surface
(C) Geothermal
(D) Earthquake
(B) Forces working on earth’s surface

Question 27.
River, wind, glacier, sea waves, etc. are agents of – processes.
(A) Endogenic
(B) Exogenic
(C) Spacial
(D) None of these
(B) Exogenic

Question 28.
An agent of degradation is –
(A) Weathering
(B) Biological action
(D) Subduction
(A) Weathering

Question 29.
An agent of agradation is –
(A) Tides
(B) Tsunami
(C) Flowing water
(D) Sea waves
(C) Flowing water

Question 30.
The process by which the landforms on the earth’s surface tends to reach a balanced profile is called –
(C) Subduction

Question 31.
The process by which natural agents reshapes the existing landscapes over the earth’s surface is known as
(A) Exogenetic
(B) Endogenetic
(C) Orogenetic
(D) Epirogenetic process
(A) Exogenetic

Question 32.
The process by which the earth surface increases is –
(C) Weathering
(D) Denudation

Fill in the blanks : 1 Mark

1. The process by which the natural forces create landforms on the earth’s surface are called ________.
2. The sources of energy for exogenic processes apart from gravitation are _______ and ________.
3. The process of aggradation and degradation together result in a _______ profile.
4. The limit of degradation or erosion is marked by the nearest ________.
5. Delta, sand beach, flood plain etc. are examples of _______ process.
6. The main controlling factor of aggradation is ________.
7. The term ‘gradation’ was first used by ________.
8. The process of _______ brings a balance between erosion, transportation and deposition.
9. An example of an endogenetic process of landform formation is ________.
10. The process of modifying landforms by combined action of erosion and weathering called ________.
1. Exogenic processes
2. Sun and atmosphere
4. Sea level
6. Slope
7. Gilbert
9. Plate movement
10. Denudation

State True or False : 1 Mark

1. Filling up of lowlands is a process of aggradation or deposition. [ ]
2. Lowering of height of highlands occurs due to degradation. [ ]
3. The main source of energy of exogenic process is the sun. [ ]
4. The main agent of gradation is river. [ ]
5. Loess plains are formed by degradation. [ ]
1. T
2. T
3. T
4. T
5. F

Answer in few words : 1 Mark

Question 1.
What are the processes of landform creation known as a whole?
Earth movements.

Question 2.
Name an agent of exogenic process.
River or glacier or wind.

Question 3.
Which process is responsible for planation or formation of plains on the earth’s surface?

Question 4.
What is the result of gradation?
Planation of the landform.

Question 5.
Which process of planation results in filling up of river beds and flooding?

Question 6.
Name the processes that cause degradation.
Erosion, transportation and mass wasting,

Question 7.
Name the main source of energy for the exogenetic process.
Sun.

Question 8.
What is the process of removal of weathered rocks to other places ?
Erosion.

Question 9.
What is the process of filling of loose materials like rocks and soil along the slope?
Mass wasting.

Question 10.
What type of weathering is most prominent is desert region?
Mechanical weathering.

Question 11.
Match the following :

 A column B column 1. Endogenetic force (a). Weathering 2. Exogenetic force (b). Delta 3. Aggeadation (c). main source is sun 4. Degradation (d). Beneath the surface

## WBBSE Class 9 Physical Science Notes Chapter 6 Heat

Comprehensive WBBSE Class 9 Physical Science Notes Chapter 6 Heat can help students make connections between concepts.

## Heat Class 9 WBBSE Notes

Heat : It is an external agency whose absorption turns a body hot and extraction turns a body cold.

Sensible heat : It is the type of heat that is perceptible by senses. This causes rise of temperature of a body that can be measured with a thermometer.

Latent heat : It is the quantity of heat absorbed or released when a substance of unit mass undergoes a physical change of state at a constant temperature and pressure.

Radiant heat : It transmits from a source of heat in all directions with the speed of light and in the form of waves.

Temperature : The temperature of a body is the thermal condition which determines whether it will absorb heat from other body or release heat to that body when they are kept in contact.

Lower fixed point of a thermometer : At normal atmospheric pressure, the temperature at which ice melts into water or pure water freezes into ice is called the lower fixed point of a thermometer.

Upper fixed point of a thermometer : It is the temperature at which pure water boils and transforms into steam under normal atmospheric pressure.

Fundamental interval : The range of temperature between the upper and lower fixed points is called fundamental interval.

Celsius scale of temperature : In this scale, the lower fixed point is 0°C and the upper fixed point is 100°C. The fundamental difference is divided into hundred equal parts and each part represents 1°C.

Fahrenheit scale of temperature : In this scale, the lower fixed point is 32°F and the upper fixed point is 212°F. The fundamental difference is divided into 180 equal parts and each part represents 1°F.

Kelvin scale of temperature : In this scale the lower fixed point is 273K and the upper fixed point is 373K, the fundamental interval is divided into 100 equal divisions like that in the Celsius scale. Each division represents 1K.

Calorie : It is the amount of heat required to raise the temperature of one gram of pure water through 1°C.

Specific heat : It is defined as the quantity of heat required to raise the temperature of unit mass of it by 1 degree.

Specific heat capacity of a substance : Specific heat capacity of a substance is the quantity of heat required to raise the temperature of 1kg of the substance through 1K.

Units of specific heat :

• CGS : calg-10 C-1
• SI : Jkg-1K-1

Thermal capacity or heat capacity of a body : It is defined as the quantity of heat needed to raise the temperature of the body for unit degree rise of temperature.

Units of heat capacity :

• CGS : calg-10 C-1
• SI : Jk-1

Water equivalent : The water equivalent of a body is the mass of water which will be heated through one degree by the amount of heat required to raise the temperature of the body through one degree.

Units of water equivalent:

• CGS: gram (g)
• SI: kilogram (kg)

Fundamental principle of calorimetry :

Conditions :

• During the process of heat transfer, there is no heat exchange with the surrounding.
• No chemical reaction takes place between the bodies.

Principle :
Heat lost by the hotter body = Heat gained by the colder body.

First law of thermodynamics : Whenever mechanical work is converted into heat energy, the heat so obtained is directly proportional to the work done.
If, ‘W’ be the mechanical work done and ‘H’ be the corresponding heat energy produced, then from first law of thermodynamics,
W α H or W = JH
where J is the constant of proportionality and is known as mechanical equivalent of heat.

Mechanical equivalent of heat : The mechanical equivalent of heat is numerically equal to the work done to produce unit quantity of heat.

Unit of mechanical equivalent of heat :

• CGS: 4.8 x 107 erg cal-1
• SI : In SI, both heat and work are measured in Joule, so mechanical equivalent of heat has no unit and its value is 1.

Change of state : There are three states of matter – solid, liquid and gas. Substances can be changed from one state to other by application or removal of heat from them. This process is known as change of state.

Mathematical expression of Latent heat : Q = mL
where Q is the amount of heat supplied (or extracted) to change the state of ‘m’ mass of substance and L is latent heat

Unit of Latent heat :

• CGS : cal g-1
• SI : J kg-1

Types of Latent heat:

• Latent heat of fusion
• Latent heat of solidification
• Latent heat of vaporisation
• Latent heat of condensation

Latent heat of fusion of ice and latent heat of solidification of water are both equal:

• CGS : 80 cal g-1
• SI: 336 × 105 Kg-1

Latent heat of vaporisation of water and latent heat of condensation of steam are both equal:

• CGS: 537cal g-1
• SI : 226 × 106 Jkg-1

Melting point : The melting point of a solid is the definite temperature at which it melts on heating under normal atmospheric pressure and the temperature remains constant until the melting is
completed.

Boiling point : The boiling point of a liquid is the temperature at which a liquid boils under normal atmospheric pressure. The boiling point of a liquid depends upon:

• The nature of the liquid
• Presence of dissolved substance
• The superincumbent pressure

pressure: Whenever a liquid evaporates at any temperature, the vapour exerts a definite pressure on everything in contact. This pressure is called vapour pressure of the liquid at that temperature.

Saturated vapour : If a liquid is allowed to evaporate in a closed space, after some time it is found that evaporation stops i.e. at a given temperature. there is a maximum limit to the amount of
vapour the space can hold. The space is said to be then saturated with vapour and the vapour is then called saturated vapour.

Unsaturated vapour : If at a given temperature, a space contains a smaller amount of vapour than the maximum possible amount that the space can hold, the space is then said to be unsaturated and the vapour is called unsaturated vapour.

Saturated vapour does not obey Charles’ law or Boyle’s law, while unsaturated vapour obeys charles’ and Boyle’s law.

Critical temperature : For every substance in gaseous state there is a certain temperature such that if the substance is below this temperature, it can be liquefied by the application of suitable pressure,
and above this temperature, it cannot be liquefied, however large the pressure may be, then the temperature is called the critical temperature for that substance.

Gas : A substance at a temperature above critical temperature is called gas.

Vapour : When the substance is at a temperature below its critical temperature it is called vapour.

Anomalous expansion of water: Usually liquids expand on heating. But in the case of water we find deviation from this general behaviour of the liquids within a certain range of temperature. It is found that if certain mass of water at an temperature about 10°C be taken and allowed to cool, its volume is observed to fall gradually till it reaches the temperature of 4°C, when with further cooling the volume of water will increase instead of decreasing.

The behaviour of water is some how different from other liquids. The volume of water is minimum at 4°C and its density is maximum at 4°C. This phenomenon is called the anomalous expansion of water. This phenomenon is called the Ienipentturi anomalous expansion of water.

Effect on marine life : Anomalous expansion of water has great practical importance on the marine life in the cold countries. In these countries when air above the surface of water of pond falls below 0°C, the water on the surface on cooling, become denser than that below and gradually sinks downwards.

This continues until the temperature of water falls to 4°C. As the surface temperature falls further it becomes less dense than the water below, which is at 4°C and is the densest. It thus remains at the top, cooling C more and more and ultimately a layer of ice is formed there and remains there as ice is lighter than water. The layer of ice forms a poor conducting layer on the top, which prevents the heat from water below to pass into colder atmosphere above.

The temperature of the deeper layers of the water in the pond remains nearly at 4°C and falls gradually to 0°C upwards till the layer of ice is reached. The marine life in water is thus saved.