# WBBSE Class 10 Physical Science Solutions Chapter 4 Thermal Phenomena

Detailed explanations in West Bengal Board Class 10 Physical Science Book Solutions Chapter 4 Thermal Phenomena offer valuable context and analysis.

## WBBSE Class 10 Physical Science Chapter 4 Question Answer – Thermal Phenomena

Very Short Answer Type Questions :

Question 1.
Is it possible for a body to have negative temperature in kelvin scale?
No, because below 0K temperature, volume of a gas would be negative which is impossible.

Question 2.
What is the SI unit of heat ?
SI unit of heat is Joule.

Question 3.
Mention the CGS unit of heat?
CGS unit of heat is calorie.

Question 4.
Is volume coefficient of a gas different from its pressure coefficient?
No, they are equal.

Question 5.
What is the value of specific heat of water in SI unit?
4200 J kg-1 K-1.

Question 6.
Is it possible that heat is supplied to a body without changing the temperature?
Yes, during change of state there is no change in temperature although heat is supplied.

Question 7.
What is the value of latent heat of fusion of ice in CGS system?
80 cal g-1.

Question 8.
Do water and ice have the same specific heat?
No, specific heat of water is 1 cal g-1 °C-1 and that of ice is 0.5 cal g-10 C-1.

Question 9.
What is difference between 1° C and 1 C° ?
1° C is a particular temperature, while 1 C° is the interval of one degree Celsius of temperature.

Question 10.
What is the lower fixed point of a celsius scale?
0° C

Question 11.
What is the upper fixed point of a Fahrenheit Scale?
212° F

Question 12.
Is there any upper fixed point in Kelvin Scale?
273.13 K, which is the triple point of water.

Question 13.
Which is more expansible-solid, liquid or gas ?
Gas.

Question 14.
A metal scale does not give correct value at all temperature-explain.
At different temperature distance between different marks of the metal scale is different due to thermal expansion of the metal.

Question 15.
The Coefficient of linear expansion of a metal is 19 × 10-6° C-1. What is its value per degree Fahrenheit ?
∝ = $$\frac{5}{9}$$ × 19 ×10-6 = 10.6 × 10-6 °F.

Question 16.
Is coefficient of linear expansion possible in the case of a liquid?
No, liquid has no definite length.

Question 17.
There is co-efficient of apparent expansion in a liquid but not in a gas-why ?
For same rise of temperature, liquid expands only about 10 times than solid, while gas expands about 100 times than solid. So expansion of vessel can be neglected in case of gases.

Question 18.
What is anomalous expansion of water?
In the range 0°C to 4°C, volume of water decrease instead of increasing, like other liquids. This is known as anomalous expansion of water.

Question 19.
Why are there two types of coefficient of expansion of a gas?
The change of temperature is very much affected by both its pressure and volume, so gas has two types of coefficient of expansion.

Question 20.
Is a temperature lower than absolute zero of temperature possible?
No.

Question 21.
What is thermal conductivity of a perfect heat conductor?
Infinite.

Question 22.
What is thermal conductivity of a perfect heat insulator?
Zero.

Question 23.
Can heat flow by canvection take place in a straight line?
In convection heat travels in straight or curved path in upward direction only.

Question 24.
Can convection take place in solid ?
No, for convection a fluid medium is required.

Question 25.
What is the absorbing power of a perfectly black body ?
One

Question 26.
What is the reflecting power of a perfectly black body ?
Zero.

Question 27.
What is a perfectly black body ?
A body which absorbs all radiations incident it.

Question 28.
By which mode the heat reaches to the earth from the Sun?

Question 29.
Explain for cooking, a black vessel is more convenient than a polished one.
Black surface is better absorber of heat.

Question 30.
Heat is generated continuously in an electric heater but its temperature becomes constant offers some time. Why?
When rate at which heat is generated by electric current becomes equal to the rate at which heat is lost by radiation, thermal equilibrium is reached and hence temperature becomes constant.

Question 31.
Why ventilator are placed near the roof at a room?
Warm air of the room becomes lighter and moves upward. So for better convection current ventilators are placed near the roof of the room.

Question 32.
Name three modes of transfer of heat.

Question 33.
Name the element which is the best conductor of heat ?
Silver.

Question 34.
What is the unit of coefficient of thermal conductivity in SI ?
Wm-1 K-1.

Question 35.
What is thermal expansion?
Dimensions of all substances generally increases with increase in temperature. This phenomenon is known as thermal expansion.

Question 36.
Name the three types of expansion in solid?
The types of expansion in solid –

1. Linear expansions
2. Superficial expansions
3. Volume expansions.

Question 37.
Define the term ‘coefficient’ of linear expansion of solld.
Coefficient of linear expansion of solids : The coefficient of linear expansion of a solid is the increase in its length per unit length per degree rise of temperature.

Question 38.
Give the SI unit of coefficlent of linear expansion.
K-1.

Question 39.
Write the relationship among α, β and γ.
α = $$\frac{β}{2}$$ = $$\frac{γ}{3}$$

Question 40.
Does unit of coefficient of linear expansion depend on unit of length?
No.

Question 41.
What is thermal conduction ?
Conduction is the process of transfer of heat through a substance without any motion of the particles of the substance.

Question 42.
Name two substances which are good conductors of heat.
Silver, Copper.

Question 43.
Name two bad conductors of heat.
Glass and wooden rod.

Question 1.
What do you mean by heat ?
Heat : It is a form of energy which produces sensation of warmth.

Question 2.
What are the different types of motion?
Different types of motions are

1. Translational motion
2. Vibrational motion
3. Rotational motion

Question 3.
What is definition of heat with respect to motion?
Definition of heat with respect to motion: Heat possessed by a body is the total thermal energy of the body and is the sum of kinetic energies of all the individual molecules forming the body due to translational, vibrational and rotational motions of the molecules.

Question 4.
What do you mean by calorie?
Calorie: It is the quantity of heat required to raise the temperature of 1 g} water through 1° \mathrm{C}.

Question 5.
What is temperature?
Temperature : It is the thermal condition of a body which would determine the direction of flow of heat, when the body is placed in thermal contact with another body.

Question 6.
What is upper fixed point of a thermometer ?
Upper fixed point : It is the temperature of steam from water boiling under a pressure of 76 cm} of mercury at sea level and 45° latitude.

Question 7.
What is lower fixed point of a thermometer ?
Lower fixed point: It is the temperature of melting ice under a pressure of 76 cm} of mercury at sea level and 45° latitude.

Question 8.
What is fundamental interval ?
Fundamental interval. The difference between the fixed points of a scale is called fundamental interval.

Question 9.
What do you mean by thermal expansion ?
Thermal Expansion: Dimension of all substances generally increases with increase in temperature. This phenomenon is known as thermal expansion.

Question 10.
What are the types of expansions in solids ?
Types of expansions in solids:

1. Linear expansions
2. Superficial expansions
3. Volume expansions

Question 11.
What is apparent expansion of the liquid ?
Apparent expansion of the liquid: If the expansion of the liquid is measured ignoring the expansion is called the apparent expansion of the liquid.

Question 12.
What is real expansion of the liquid ?
Real expansion of the liquid: When the actual expansion of the liquid is measured by considering the expansion of the containing vessel, it is called real expansion of the liquid.

Question 13.
What is the conclusion of Hope’s experiment ?
Conclusion of Hope’s experiment: From Hope’s experiment it is proved that water at bottom which is densest at 4°C. After sufficiently long time the temperature of the lower thermometer falls slightly due to loss of heat by conduction to the upper regions.

Question 14.
What is molar specific heat at constant volume (Cv) ?
Molar specific heat at constant volume (Cv) : The molar specific heat of a gas at constant volume (Cv) is the amount of heat required to raise the temperature of one mole of the gas through one degree keeping the volume constant throughout.

Question 15.
What is molar specific heat at constant pressure (Cp) ?
Molar specific heat at constant pressure (Cp) : The molar specefic heat of a gas at constant pressure (Cp) is the amount of heat required to raise the temperature of one mole of the gas through one degree keeping the pressure constant throughout.

Question 16.
What is water equivalent of a body ?
Water equivalent: Water equivalent of a body is the mass of water which will be heated through one degree by the amount of heat that raises the temperature of the body through one degree.

Question 17.
What is Regelation ?
Regelation: The phenomenon of melting of ice under pressure and freezing again on releasing the pressure is called regelation.

Question 18.
What do you mean by vapour pressure of a liquid ?
Vapour 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.

Question 19.
What is conduction of heat ?
Conduction: It is the process of the transfer of heat through a substance without any detectable motion of the particles of the substance.

Question 20.
What is convection of heat ?
Convection of heat: It is the process by which heat is transmitted through a liquid or gas from a hotter point to a colder point due to the bodily motion of the heated particles of the substances.

Question 21.
What is Radiation of heat ?
Radiation: It is the transmission of heat from a hot body to a cold body without the help of any medium and without appreciable heating at the intervening medium if any.

Question 22.
What is perfectly black body ?
Perfectly black body: A perfectly black body is that which absorbs completely the radiations of all the wavelengths on it.

Question 23.
What is green house effect ?
Green house effect: Green house effect is an example of selective absorption of heat by glass. The amount of heat transmitted through a substance depends on temperature of the source of heat.

Question 24.
What do you mean by global warming ?
Global warming: Carbon dioxide, water vapour, methane, nitrus oxide, tropospheric ozone, chlorofluoro carbon compounds, halogens campounds etc. on increasing the amount of greenhouse gases in the atmosphere, the temperature of earth increases. It is known as global warming.

Question 1.
State the units and dimensions of different coefficient.
The unirs and dimensions of different coefficient.

Question 2.
What is anomalous expansion of water ?
Aromalous expancion 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. The volume of water is minimum at 4°C and hence its density is maximum at 4°C. This phenomenon is called the anomalous expansion of water.

Question 3.
What is the fundamental principle of calorimetry ? What are the conditions ?
Fundamental principle of calorimetry:
Heat lost by hot body = Heat gained by cold body.
Cotditicns: (i) during the process of heat transfer, there is no heat exchange with the surrounding.
(ii) no chemical reaction takes place between the bodies.

Question 4.
What is thermometric conductivity ?
Thermometric conductivity: The rate of rise of temperature during the variable state is proportional to K/ps (where K = thermal conductivity of the material, Ps = specific heat). This ratio is known as thermometric conductivity or the thermal conductivity per thermal capacity per unit volume.

Question 5.
Give few applications of conductivity ?
Applications of conductivity:
(i) Ice is packed in saw dust, because air which is bad conductors of heat being trapped in the saw dust prevents transfer of heat from the surrounding to the ice. So ice does not melt.
(ii) Cooking utensils are provided with wooden or plastic handles, as wood or plastic are bad conductors of heat, so we can hold the hot utensiles with the help of these handles.
(iii) In winter, birds often swell their feathers, ther by enclosing air between their bodies and feathers and thus does not allow flow of heat from the bodies of the birds and keeps them warm.

Frain Storing Questions :
Very Short Answer Type Questions :

Question 1.
The value of α for iron is 1.2 × 10-5. What do you mean by that?
This means 1 cm of an iron rod (at 0°c) expands linearly by 1.2 × 10-5 cm for 1°C rise in temperature.

Question 2.
Name two devices which use bimetallic strip.
Automatic fire alarm and thermostat.

Question 3.
The diameter of an iron tyre is kept slightly smaller than the wooden wheel on which this tyre is to be mounted. why?
The diameter of an iron tyre is kept slightly smaller than the wooden wheels because of heating, the iron tyre expands and perfectly fits over the wooden wheels.

Question 4.
Between apparent and real expansion coefficients of a liquid which one is its own characteristic?
Apparent expansion of liquid happens simply because the container expands. Therefore, real expansion coefficient of a liquid is its own characteristic.

Question 5.
How δr is related to δa & δg ?
The relation is :
δr = δa + δgr = Real expansion of liquid
δa = Apparent expansion of the liquid
δg = Volume expansion of the container)

Question 6.
What is the conductivity for vacuum ?
Conduction does not take place through vacuum. So, pure vacuum has zero conductivity.

Question 7.
What is thermal resistivity?
Reciprocal of coefficient of thermal conduction is called thermal resistivity ($$\frac{1}{K}$$).

Question 8.
What is the unit of thermal resistivity?
The unit of thermal resistivity is j-1 m.k.s

Question 9.
What should be the value of thermal conductivity for an ideal conductor ?
The value of thermal conductivity for an ideal conductor is infinite.

Question 10.
Write the dimension of thermal conductivity (K)

Numerical Problems

Example 1:
On a certain day the maximum temperature was found to be 120°F. What is it in celsius scale?
We know that
$$\frac{C}{5}$$ = $$\frac{F-32}{9}$$
Let 120°F = x°C
or, $$\frac{x}{5}$$ = $$\frac{120-32}{9}$$
or, x = 48.9°C

Example 2:
A thermometer reads 5° in melting ice and 99° in dry steam at normal pressure. Find the temperature on the Fahrenheit scale when the thermometer reads 52°.
Let the temperature in the Fahrenheit scale be x°F corresponding to 52° in the faulty thermometer whose fundamental interval in 99° – 5° = 94°. Thus,

or,
x = 90 + 32 = 122°F

Example 3:
Find the temperature at which the reading in Fahrenheit scale is double of the reading in the celsius scale.
Let x°C = 2 x°F
We know $$\frac{C}{5}$$ = $$\frac{F-32}{9}$$
or, $$\frac{x}{5}$$ = $$\frac{2 x-32}{9}$$
or, x = 160°C and 2 x = 320°F

Example 4:
What is the reading of a Fahrenheit thermometer when a centigrade thermometer reads 25°C ? The temperature of a body is raised by 25°C. What is the value of this rise of temperature in Fahrenheit scale?
We know, $$\frac{C}{5}$$ = $$\frac{F-32}{9}$$
We have, $$\frac{25}{5}$$ = $$\frac{F-32}{9}$$
∴ F = 45 + 32 = 77°F
We know, 1 division on centigrade scale = $$\frac{9}{5}$$ division on the Fahrenheit scale
∴ 25°C = $$\frac{9}{5}$$ × 25 = 45°F

Example 5:
Find the increase in energy per atom of aluminium when temperature of a piece of aluminium increases by 1° C .27 g of aluminium contains 6 ×1023 atoms and its specific heat is 0.2 .
Let us take 27 g of aluminium heat absorbed by it in raising its temperature by 1°C = 27 × 1 × 0.2 = 5.4 cal
= 5.4 × 4.2 J
Now, 27 g of aluminium contains 6 ×1023 atoms
Thus, energy per atom = $$\frac{5.4 ×4.2}{6 ×1023}$$ = 3.78 × 10-23 J

Example 6:
Two rods, one of glass and the other of steel, are of equal length of 0°C. At 100°C they differ in length by 1 mm. Find their length at 0°C. Given α for glass = 8 × 10-6 C and α for steel = 12 ×10-6 C-1.
Let length of each rod l0 m at 0° C and at 100° C. Let the lengths of glass and steel rod be l g and l s metres respectively.
This, ls = l (1 + 8 × 10-6: 100) and ls = l0(1 + 12 × 10-6 × 100)
∴ ls – lg + l0 × 1 v-4(12-8) = 4 × 1 J-4 l0
Now, ls – ls = 1 mm = 10-3 m
So, 10-3 = 4 × 10-4 l0
∴ l0 = 25 m

Example 7:
Two vessels connected by a thin pipe with a sliding plug contain a liquid at temperature 20° C and 80° C. What is the ratio of the heights of liquid columns in the vessel if the coefficient of volume expansion of the liquid be 10-3 °C-1 ?