**Important questions of thermal properties of matter**

*This assignment provides all important questions of this chapter , which will be important for examinations point of view.*

1. Briefly describe the various scale of temperature and give the relation between them.

2.Define coefficient of linear ,area and volume expansion , also find the relation between them.

3.Show with the help of potential energy diagram that thermal expansion in solid is due to increase in interatomic distance.

4. What do you mean by the term thermal stress? Derive an expression for the same in case of a road fixed at both ends.

5. Define heat capacity, molar heat capacity and specific heat capacity also give their units and dimensions.

6. What do you mean by the term latent heat of fusion and latent heat of vaporization ?

7.Using P-T diagram of water , discuss the behavior of water when both pressure and temperature are (i) above the triple point (ii) at triple point (iii)below the triple point.

8. What is thermal conduction ? Discuss the variable and steady state of a rod being heated at one of its ends.

9. Define the coefficient of thermal conductivity and explain the formula used . Why do metals have higher conductivity then insulator?

10. Write the expression for the rate of flow of heat energy through a conductor maintained at different temperature at its two ends . Explain the symbols used . Given that heat is measured in joule , derive the units of thermal conductivity.

11.What is Newton’s law of cooling / how can it be experimentally verified? Plot the graph of log (T-T_{0}) V/S time ‘t’.

12.Discuss energy distribution in the spectrum of perfectly black body. What conclusion do you derive from this distribution? Also explain the Wine’s displacement law of radiation.

13. State and explain Stefan’s law . How will you deduce Newton’s law of cooling from this law?

14. State and prove Kirchhoff’s law of heat radiation . Explain how Kirchhoff’s law leads to the conclusion that good absorber are good emitters.

Numericals-

1. A surveyor uses a steel measuring tape that is exactly 50m long at a temperature of 20^{0}C . What is the length on the hot summer day when the temperature is 35^{0}C? coefficient of linear expansion is 1.2 x 10^{-5}K^{-1. }_{. }[ans-50.009m]

2. A glass flask with volume 200cm^{3} is filled to the brim with mercury at 20^{0}C . How much mercury overflows when temperature of the system is raised to 100^{0}C ?[α for glass is 0.40x 10^{-5}K^{-1}.and cubical exp. For mercury is 1.2x 10^{-5}K] . Ans-2.7cm^{3}].

3. A pendulum clock consist of an iron rod connected to a small heavy bob. If it is designed to keep correct time at 20^{0}C, how fast or slow will it go in 24 hours at 40^{0}C. ( α for iron is 1.2×10^{-5}K^{-1}). Ans-10.4 sec

4.At what temperature is the Fahrenheit scale reading equal to(I) half that on the Celsius scale (II)Equal to the reading on Celsius scale?

5.A faulty thermometer reads 5^{0}C in melting ice and 99^{0}C in steam . Find the correct temperature in ^{0}F when this faulty thermometer reads 52^{0}C.

6.

An iron bar of length l_{1}=0.1m, A_{1}=0.02m^{2}, k_{1}= 79w/mK and a brass bar of length l_{2}=0.1m area 0.02m^{2} and K_{2}=109 W/mK are soldered end to end as shown in fig. the free ends of the iron ball and brass bar maintained at 373K and 273K respectively . Obtain expression for and hence compute (a) the temperature of the junction(b) the equivalent thermal conductivity of the compound bar and (c)the heat current through the compound bar. Ans-315K ,91.6W/mK, 916W.

7. A body cools from 70^{0}c to 50^{0}C in 6 minutes and to 40^{0}C in 12 minutes . Find the temperature of the surroundings if cooling occur according to Newton’s law of cooling. Ans-30^{0}C.

8. A pan filled with hot food cools from 94^{0}C to 86^{0}C in 2 minutes when the room temperature is 20^{0}C . How long will it take to cool from 71^{0}C to 69^{0}c . Ans- 42sec.

9. The energy emitted per second by a black body at 1227^{0}C is E . If the temperature of the black body is increased to 2727^{0}C , calculate the energy emitted per second in terms of E in the second case. Ans-16E

10. Calculate the temperature in kelvin scale at which a perfectly black body radiates at the rate of 5.67 W/cm^{2}. Given σ=5.67×10^{-8}W/m^{2}K^{4}. Ans-1000K.