# WBBSE Class 7 Geography Solutions Chapter 3 Air Pressure

Detailed explanations in West Bengal Board Class 7 Geography Book Solutions Chapter 3 Air Pressure offer valuable context and analysis.

## WBBSE Class 7 Geography Chapter 3 Question Answer – Air Pressure

Multiple Choice Questions & Answers : ( 1 mark for each question)

Question 1.
Which is false, air is-
i) colourless
ii) odorless
iii) volumeless
iii) volumeless

Question 2.
Which is false, molecules are visible in-
i) solid
ii) gas
iii) liquid
ii) gas

Question 3.
With the increase of altitude the air pressure and temperature –
i) decreases
ii) increases
iii) remains same
iv) may increase or decrease
i) decreases

Question 4.
The air pressure in equitorial and tropical regions are –
i) medium
ii) low
iii) high
iv) may be high or low
ii) low

Question 5.
High pressure areas usually experience the weather-
i) cloudy
ii) rainy
iii) stormy
iv) calm
iv) calm

Question 6.
Example of a violent fast wind-
i) syclone
ii) hurricane
iii) typhoons
iv) all the winds
iv) all the winds

Question 7.
Low pressure areas usually experience the weather-
i) stormy
ii) clear sky
iii) calm
i) stormy

Question 8.
The imaginary line which connect equal pressure region in weather map is known as –
i) isobar
ii) isotherm
i) isobar.

Question 9.
The region where temperature remain high, there prevails-
i) high pressure
ii) low pressure
low pressure.

Question 10.
Moist air is-
i) lighter
ii) heaver than dry air
lighter

Fill in the blanks : (I mark for each question)

1. The hight of the Mount Everest is ________.
8848m.

2. The air pressure is almost per ________ square centimeter.
1 kg.

3. ________is an important factor to determine the weather and in our day to day life.
Air pressure.

4. Air pressure ________ with the increasing of altitude.
reduces.

5. The air exerts pressure to ________ derection.
all.

6. ________ is used for measuring air presure.
Barometer.

7. The density of air ________ with the increasing of altitude.
decreases.

8. The air gets heated by ________ process.
three.

9. In the cooler region of Earth’s surface ________ pressure prevails.
high.

10. Water vapour remains very ________ in cooled and heavy air.
low.

11. Isober expressed in ________.
Milibar.

12. Volume of air changes with the ________.
change of temperature.

13. Moist air is ________ than dry air.
lighter.

14. Air pressure is maximum on ________ of the earth.
sea surface.

15. Low pressure generate around equator and high pressure in both the ________.
tropics.

State whether True or False : ( 1 mark for each question)

1. Air has mass and volume.
true

2. The air pressure per square foot is about weight of one tonne of material.
true

3. Molecules in solid and liquid are not visible.
false

4. Air pressure is very significant in our daily lives.
true

5. Air pressure at sea level is equal to that of a 72 cm column of mercury.
false

6. Moister-laden air is heavier than dry air.
false

7. Warm air expands and starts to move upwards. is
true

8. Isobar represent air pressure meacured in milibars. is
true

9. High pressure areas usually experience cloudy weather.
false

10. Air in low pressure area is usually light and expanding.
true

11. Air flows from high pressure to those of low pressure.
true

12. The The instrument used to measure air pressure is called Barometer.
true

Match the column A with column B.

 Column A Column B a) There is some air i) low air pressure b) Molecles in solid ii) heavier c) There is no air iii) towards the surface of the earth d) Boiling point of water drops iv) are visible e) Turbulent weather is a result of v) weather in low pressure areas f) Cold polar regions have vi) in our body g) Dry air is vii) higher air pressure h) We have cloudy, stormy viii) in the space i) Cloud and heavy air sinks ix) in mountanious regions

a) There is some air in our body.
b) Molecles in solid are visible.
c) There is no air in the space.
d) Boiling point of water drops in mountanious regions.
e) Turbulent weather is a result of low air pressure.
f) Cold polar regions have higher air pressure.
g) Dry air is heavier.
h) We have cloudy, stormy weather in low pressure areas.
i) Cloud and heavy air sinks towards the surface of the earth.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
How much presure does air exert per square ft ?
Air exerts the pressure of 1 tonne per square ft.

Question 2.
Why is the space suit of astronauts filled with air.
There is no air in space. So to keep the balance in pressure between internal air pressure and the outer air the spacc suit of astronaut filled with air.

Question 3.
Why is the air pressure maximum on sea surface?
The air pressure is maximum on sea surface because the gravitational pull is maximum in sea surface.

Question 4.
What is the air pressence of sea surface?
The air pressure on sea surface is 101325 ml.

Question 5.
Who discovered the mercury Barometer?
The scientist Torricelli discoming the mercury Barometer.

Question 6.
How does the mercury level react if the pressure increases?
If the pressure increase the mercury level also increases.

Question 7.
How does the air pressure vary with the increasing of every 110 altitude.
With the increasing of every 110 m altitude to the air pressure reduces equal to 1 cm mercury level.

Question 8.
What is isobar?
The imaginery line which connect equal pressure region in weather map is known as isobar.

Question 9.
Where is the rotational speed is maximum on the Earth?
The rotational speed is maximum in and around equator.

Question 10.
Why there are problems of boiling of cooking anticles in high altitude?
In high altitude the boiling point is less then 100° C that causes problems of boiling of cooking articles in high altitude.

Question 11.
Why does the astronauts carry oxygen cylinders with them?
At high altitudes air with oxygen becomes scarce, so astronauts carry oxygen cylinders with them.

Question 12.
Which air is lighter-moister-laden or dry air?
Moister-laden air is lighter than dry air.

Question 13.
Where is the speed of earth’s rotation highest?
The speed of earth’s rotation is highest at the equator.

Question 14.
Where does stormy and turbulent weather prevail?
Stormy and cloudy weather prevails in low pressure areas.

Question 15.
What kind of air is formed in a high pressure area?
In a high pressure area air is sold and compact..

Short Questions & Answers : (2 marks for each question)

Question 1.
What is air pressure? How can it be clasiffied.
In certain place on the earth surface the layers of air exerts pressure per square centimeter which is known as air pressure. There are two types of air pressure high pressure and low pressure.

Question 2.
Why do we not feel the air pressure.
In spite of living in water the fish can not feel the pressure of water. Similarly in spite of living in the lowest layer of air we can not feel the air pressure. This is because our body pressure and the atmospheric prerssure is equal.

Question 3.
The air exerts pressure-Prove it with an experiment.
Take a glass full of water and place a post card to cover the glass. Now if we turn over the glass we see the post card sets firmly on the glass and water remain as it. It proves that the air exerts pressure over the post card in upward direction.

Question 4.
What are high pressure and low pressure region?
In which places the air pressure is more than that of surrounding area is called high pressure region. On the orther hand in which places the air pressure is lesser than that of surrounding areas is called low pressure region.

Question 5.
What will be the weather of two places? If you travel from the Puri beach to Mount Everest, what types of changes in your daily life are likely to happen?
As the Mount everest is higher than the sea level the temperature is lesser than Puri. Thus the climate of Mount Everest is very cold if we travel from Puri to Mount Everest we have to use wollen cloths due to the cold climate.

Question 6.
What is the cause of variation in air presure.
Circulation of air in the atmosphere is caused by pressure differences generated primarily by uneven isolation Air flows from areas higher pressure to areas of lower pressure.

Question 7.
What is the normal range for air pressure?
A metric unit has been defined to describe normal atmospheric pressure, called a bar, and the instrument become a barometer. Normal average sea-level pressure is 1.o1325 bars.

Long Questions & Answers : (3 marks for each question)

Question 1.
What is isobar? What are its characteristics?
Isobar is the imaginary line which connects equal pressure region in weather map. The characteristics of isobar are-

1. The unit in which isobar is expressed is milibar. The normal air pressure over the Earth varries from 980 to 1050 ml.
2. It is expressed according to the presure on sea level.
3. They never intersects or touch one another.
4. The difference of air pressane is maximum when the lines of isobars are very closed to each other.

Question 2.
What are the characteristics of high presure.
The characteristics of this high pressure are:

1. The high pressure is created when the temperature of air islow. Thus the high pressure prevails mountain region and cold polar region.
2. For being cold the air of high pressure region is compressed.
3. High pressure develops due to the decending nature of air. Thus cold air goes down in the cold region, the denisity of air increases and pressure also increases.
4. The water vapour present in cool and heavy air is very low. That is why the cloud, rain etc are not occured in high pressure rigion.

Question 3.
What are the characteristics of low pressure.
The characteristics of low prresure are-

1. The low pressure creates for the increasing of the temperature of air. Low pressure is found in Equoatorial and tropical region.
2. The air in low pressure region is light and expanded.
3. In the hot region the air on the earth’s surface gets heated and rises up. Thus the density of air near the earth surface decreases and the air pressure also decreases.
4. The water vapour in hot air condensed into water droped or ice when the air comes contact of cold air at upper layer. So the cloud formation, rain storm and rough weather occured in low pressure area.

Question 4.
What are the causes for the variation of air pressure.
The causes for the variation of air pressure are-
i. The amount of water yapour in air: The water vapour is lighter than dry air. So the water vapour containing air is lighter and exerts less pressure than dry air. This is why in rainy season the air pressure decreases than in summer.

ii. The temperature of air: Like other substance the air expands in getting heated and the density of air decreases. Then the air becomes lighter. The light air exerts less pressure and the capasity of holding water vapour increases when the air becomes hot. So at the places where waer bodies are more the air becomes wet and exerts less pressure. On the other hand the capasity holding air of cold air is less, thus it exerts more pressure. Therefore the air pressure is more in winter than in summer.

iii. The altidude: The air has many layers. The layers lie one above another. So the upper atmospheric layers exerts force on the lowest level that lies closest to the earth surface. So the density of the level is meny high and the density is gradually decreased with the altitude. The weight of the air with low density is lesser and thus. it exerts less pressure. So as proceed to the high altitude from the sea level the air pressure decreases.

iv. The depth of the atmosphere: The air pressure varies due to the variation of the depth of atmosphere. The 90% eliment of the atmosphere are present within 16 km from the earth surface. So the depth of the atmosphere that prevails on the sea level is not present on high mountain. So the depth of the air and atmospheric pressure decreases with the altitude.

Question 5.
Describe the different pressure belt of Earth.
The temperature of the air in different places is determined by the angle in which the sunrays fall on the earth. According to the different temperature of this air the Earth is divided into different pressure belt. But the pressure belts shift a little with the season change. The differnce of air pressure causes the wind blows. There are two types of air pressure.
i) High pressure and low pressure: According to air pressure the Earth is devided into seven permanent pressure belt. They are as fallows :

ii) Equatorial low pressure belt : The sun rays fall directly on the both side of the equator between 5°-10°north and south. The air of this region is hot and light. On the other hand the water body is more than the land mass here. This waters body gets healed by the tremendous heat of the sun and the water vapour rises up and mixes with to air. Thirdly – due to the rotation of the earth the air of the region gets deflected to the north and south. Thus this region is the most powerful low pressure belt.

iii) Sub tropical high pressure belt: This pressure belt lie to the both side of tropic of cancer and in the northern hamisphere and to the both side of tropic of capricorn in southern himsphere. The hot air of equatorial region rises up an gets cool there. Then its became heavy and came down to this two tropical region resulting high pressure belt.

iv) and (v) Polar high pressure belt: The speed of rotation of the Earth is minimum near the pole. Besides dwtethis. Slanting sun rays the water vapour is less in this region. The day and night’s one with a span of six months. Therefore the region remains ice capped through out the year. The density of the air is high that creats high pressure belt.

vi) and (vii) : Sub polar low pressure belt : At 60°-65° latitude of two hemisphere the low pressure belt is created due to the deflectic of the air.

Question 1.
Write the characteristics of high pressure.

1. Places with lower temperature, like the cold temperate and polar regions, have high air pressure.
2. Air in a high pressure area is usually cold and compacted.
3. Cold and heavy air naturally sinks towards the surface of the earth, gets denser and exerts higher pressure.
4. Cold and dense air is generally dry. So high pressure areas usually do not experience cloudy or rainy weather. Calm weather and clear sky prevail here.

Question 2.
Write the characteristics of low pressure.

1. Places with higher temperature, like the equatorial and tropical regions, have low air pressure.
2. Air in a low pressure area is usually light and expanding.
3. In warm areas, air near the surface of the earth gets heated and becomes light. Thus it rises and the ascent of air creates low pressure.
4. The water vapour in hot air is condensed as the air cools down in high altitude. Hence water droplets or snow/ ice is formed. This is why we have cloudy, rainy, stormy and turbulent weather in low pressure areas.

Question 3.
What is the cause of flow of air?
Air flows from areas of high pressure to those of low pressure. This proves that the difference in pressure between two areas is mainly responsible for the flow of air between them. Also, it is this flow that helps in maintaining the balance between high and low pressure zones on the earth’s surface. The more is the pressure difference, i.e. the lower the air pressure in the low pressure zones, the more is the speed of the wind blowing into that zone from the surrounding high pressure areas to keep up the balance of air pressure. When devastation is caused to life and property by violent fast winds, then those winds are known as cyclones, typhoons, hurricanes, tornadoes etc.

Question 4.
Write the causes of variation of air temperature.
Volume and density of air change with changes in temperature. The air molecules get activated by heat and start moving apart. Thus, warm air expands, gets lighter and starts to move upwards. Its density is also reduced. So the number of molecules in a specific volume of air is also reduced. This reduces air pressure. When air cools down, it shrinks and its density increases. This increases air pressure. This is why the cold polar regions have higher air pressure but the hot equatorial region has low air pressure.

Gravity and pressure of overlying air lead to greater density and therefore, greater pressure of air near the earth’s surface. These molecules disperse with altitude and the air becomes gradually less dense and exerts less pressure. This is the reason why the boiling point of water drops in mountainous regions. That is, water starts boiling at a temperature below 100° C when the air pressure drops.

Moisture-laden air is lighter than dry air. So, it exerts less pressure. Rainy, stormy, turbulent weather is actually a result of the low air pressure that is generated by moisture-laden air. Dry air is heavier and leads to the formation of high air pressure condition.

Question 5.
Is air pressure the same everywhere?