NCERT Class 11 Physics Chapter 12 Thermodynamics CBSE Board Sample Problems

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Question 7:

Which of the processes described below are irreversible?

(a) The increase in temprature of an iron rod by hammering it.

(b) A gas in a small container at a temprature is brought in contact with a big reservoir at a higher temprature which increases the temprature of the gas.

(c) A quasi-static isothermal expansion of an ideal gas in cylinder fitted with a frictionless piston.

(d) An ideal gas is enclosed in a piston cylinder arrangement with adiabatic walls. A weight W is added to the piston, resulting in compression of gas.


(a), (b) and (d).

Question 8:

An ideal gas undergoes isothermal process from some initial state i to final state f. Choose the correct alternatives.





Answer: (a), (d)

Question 9:

Figure 12.5 shows the P-V diagram of an ideal gas undergoing a change of state from A to B. Four different parts I, II, III and IV as shown in the figure may lead to the same change of state.

P-V diagram

P-V Diagram

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(a) Change in internal energy is same in IV and III cases, but not in I and II.

(b) Change in internal energy is same in all the four cases.

(c) Work done is maximum in case I

(d) Work done is minimum in case II.

Answer: (b), (c)

Question 10:

Consider a cycle followed by an engine (Fig. 12.6)

Consider a cycle

Consider a Cycle

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1 to 2 is isothermal

2 to 3 is adiabatic

3 to 1 is adiabatic

Such a process does not exist because

(a) Heat is completely converted to mechanical energy in such a process, which is not possible.

(b) Mechanical energy is completely converted to heat in this process, which is not possible.

(c) Curves representing two adiabatic processes don’t intersect.

(d) Curves representing an adiabatic process and an isothermal process don’t intersect.

Answer: (a), (c)

Question 11:

Consider a heat engine as shown in Fig. 12.7. and are heat added to heat bath and heat taken from in one cycle of engine. W is the mechanical work done on the engine.

A heat engine

A Heat Engine

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If , then possibilities are:





Answer: (a), (c)