Ch-08 – Thermal Properties of Matter
Here this post contains Short Question and Answers of Chapter 08. 5th Chapter of Physics is "Thermal Properties of Matter". Learn these question answers and other related stuff for exam preparation.
1. Why does flow from hot body to cold body?Answer : Heat flow from hot body to cold body to attain the condition of thermal equilibrium.
2. Define the term heat and temperature.Answer : Heat: Heat is the energy that is transferred from one body to the other in thermal contact with each other as a result of the difference of temperature between them.
Temperature: Temperature of a body is the degree of hotness or coldness of the body.
3. What is meant by internal energy of a body?Answer : The sum of kinetic energy and potential energy associated with the atoms, molecules and particles of a body is called its internal energy.
4. How does heating affect the motion of molecules of a gas?Answer : By heating the gas, its molecules get high kinetic energy and start to collide more randomly. And motion of gas molecules is increased by heating. So pressure of gas molecules increase by heating.
5. What is a thermometer? Why mercury is preferred as a thermometric substance?Answer : A thermometer is a device which is used to measure the temperature of a body. Mercury is preferred as a thermometric substance due to following properties.
- It is easily visible.
- It has uniform thermal expansion.
- It has low freezing point and high boiling point.
- It has a small specific heat capacity.
Answer :
Volume Thermal Expansion: The volume of a solid changes with the change in temperature and is called volume thermal expansion or cubical thermal expansion.
Explanation: Consider a solid of initial volume V0 at certain temperature T0. On heating, the solid of a temperature T, let its volume becomes V, then.
Original volume of the solid= V0
Volume of the solid after heating = V
Increase in volume of the solid = ∆V =V-V0
Original Temperature of the solid = T0
Temperature of the solid after heating = T
Increase in Temperature of the solid = ∆T = T-T0
Factors on which volume expansion depends:
Volume expansion depends on two factors.
Original volume: It is found that change in volume of a solid is directly proportional to its original volume V0.
∆V∝ V0 ————– (i)
Change in Temperature: It is found that change in volume of the solid is directly proportional to change in temperature ∆T.
∆V ∝ ∆T ————— (ii)
By Combining eq (i) and (ii), we have;
∆V ∝ V0 ∆T ———- (iii)
To change the sign of proportionally into equality a constant is used;
So,
∆V = β V0 ∆T ——- (iv)
Co-efficient of volume thermal expansion: In this equation β is called the co-efficient of volume thermal expansion of the substance.
Value of co-efficient of volume thermal expansion can be found out by using following relation.
Β = ∆V/V0∆T
7. Definition of co-efficient of volume thermal expansion:Answer : The co-efficient of volume thermal expansion β can be defined as the fractional change in its volume per Kelvin change in temperature.
Value of V: By using equation (iv) we can determine the value of V as following.
∆V = β V0 ∆T
As we know;
∆V =V-V0
So,
V-V0 = β V0 ∆T
V= V0 + β V0 ∆T
V = V0 (1+ β ∆T).
Answer : The specific heat of a substance is the amount of heat required to raise the temperature of 1kg mass of that substance through 1K.
Specific heat of any substance can be found out by using following formula:
c = ∆Q/m∆T
c is the specific heat capacity
∆Q is the amount of heat absorbed by the body
m is the mass of the body.
∆T is the change of temperature
Answer : Latent heat of fusion: Heat energy required to change unit mass of a substance from solid to liquid state at its melting point without change in its temperature is called its latent heat of fusion denoted by Hf.
Explanation: For the explanation of latent heat of fusion following terms should be understood by us.
Melting of fusion: When a substance is changed from its solid state to liquid state by adding heat, the process is called melting or fusion.
Fusion point or melting point: The temperature at which a solid starts melting is called its fusion point or melting point.
Freezing point: When a liquid is cooled, it changes into solid state. The temperature at which a substance changes from liquid to solid is state is called its freezing point.
Melting points of different substances:
Different substances have different melting points. However, the freezing point of a substance is the same as its melting point.
Formula: Hf = ∆Qf/.m or
∆Qf = mHf
In this equation
Hf is the latent heat of fusion ‘m’ is the mass of the substance.
Latent heat of fusion of ice:
Ice changes at 0oC into water. Latent heat of fusion of ice is 3.36 x 105jkg-1. That is 3.36 x 105 joule heat is required to melt 1kg of ice into water at 0oC.
10. Define latent heat of vaporization.Answer : The quantity of heat that changes unit mass of a liquid completely into gas at its boiling point without any change in its temperature is called its latent heat of vaporization denoted by Hv.
Hv = ∆Qv/m
11. What is meant by evaporation? On what factors the evaporation of a liquid depends? Explain how cooling is produced by evaporation.Answer : Evaporation: Evaporation is the changing of a liquid into vapours (gaseous state) form the surface of the liquid without heating it.
Factors which affect on evaporation:
The rate of evaporation is affected by the following factors.
- Temperature (ii) Surface area
- Nature of the liquid (iv) Wind
Evaporation causes cooling:
As evaporation takes place, fast moving molecules escape out from the surface of the liquid. Molecules that have lower kinetic energies are left behind.
This lowers the average kinetic energy of the liquids molecules and the temperature of the liquid. Since temperature of a substance depends on the average kinetic energy of its molecules, therefore the temperature of the liquid decreases.
12. Define internal energy.Answer : Internal Energy: The sum of kinetic energy and potential energy associated with the atoms, molecules and particles of a body is called its internal energy.
13. Define heat and temperature.Answer : Heat: Heat is the energy that is transferred from one body to the other in thermal contact with each other as a result of the difference of temperature between them.
Temperature: Temperature of a body is the degree of hotness or coldness of the body.
14. What are the factors on which internal energy depends?Answer : Internal energy depends upon the following factors.
- Mass of the body.
- E. of molecules of a body
- E. of molecules of a body
Answer : Heat: Heat is the energy that is transferred from one body to the other in thermal contact with each other as a result of the difference of temperature between them.
Internal energy: The sum of kinetic energy and potential energy associated with the atoms, molecules and particles of a body is called its internal energy.
16. What will be temperature on Kelvin scale of temperature when it is 20oC on Celsius scale?Answer : C = 20oC
As T = 273 +C
T = 273+ 20 = 293 K
Answer : F =100oF
Since 1.8C = F-32
1.8C=100-32
1.8 C = 68
C=68/1.8
C = 37.8oC
Thus 100oF is equal to 37.8oC.
18. Write two scales of temperature.Answer :
- Celsius Scale
- Fahrenheit Scale
Answer : A thermometer is a device which is used to measure the temperature of a body.
20. Changes 300K on Kelvin into Celsius scale.Answer : T = 300K
C = T(K) – 273
C = T(300– 273)
C =27oC
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