# Assertion and Reason Questions for Class 11 Physics Chapter 12 Thermodynamics

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Assertion and Reason Questions for Class 11 Physics Chapter 12 Thermodynamics

Directions: Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If the assertion and reason both are false.

Q.1. Assertion : When a bottle of cold carbonated drink is opened, a slight fog forms around the opening.
Reason : Adiabatic expansion of the gas causes lowering of temperature and condensation of water vapours.

Answer Answer: (a) When a bottle of cold carbonated drink is opened. A slight fog forms around the opening. This is because of adiabatic expansion of gas causes lowering of temperature and condensation of water vapours.

Q.2. Assertion : The heat supplied to a system is always equal to the increase in its internal energy.

Reason : When a system changes from one thermal equilibrium to another, some heat is absorbed by it.

Q.3. Assertion : In adiabatic compression, the internal energy and temperature of the system get decreased.
Reason : The adiabatic compression is a slow process

Answer Answer: (d) Adiabatic compression is a rapid action and both the internal energy and the temperature increases.

Q.4. Assertion : In isothermal process whole of the heat energy supplied to the body is converted into internal energy.
Reason : According to the first law of thermodynamics ΔQ = ΔU.

Q.5. Assertion : We can not change the temperature of a body without giving (or taking) heat to (or from) it.
Reason : According to principle of conservation of energy, total energy of a system should remains conserved.

Answer Answer: (d) We can change the temperature of a body without giving (or taking) heat to (or from) it. For example in an adiabatic compression temperature rises and in an adiabatic expansion temperature false, although no heat is given or taken from the system in the respective changes.

Q.6. Assertion : The specific heat of a gas is an adiabatic process is zero and in an isothermal process is infinite.
Reason : Specific heat of a gas in directly proportional to change of heat in system and inversely proportional to change in temperature.

Q.7. Assertion : Reversible systems are difficult to find in real world.
Reason : Most processes are dissipative in nature

Answer Answer: (a) In a perfectly reversible system, there is no loss of energy. Losses can be minimised, friction can be reduced, the resistance in L-C oscillating system can also be negligible. But one cannot completely eliminate energy losses. This makes a perfectly reversible system, an ideal.

Q.8. Assertion : Air quickly leaking out of a balloon becomes coolers
Reason : The leaking air undergoes adiabatic expansion.

Q.9. Assertion : Thermodynamic process in nature are irreversible.
Reason : Dissipative effects can not be eliminated.

Answer Answer: (a) In reversible process, there always occurs some loss of energy. This is because energy spent in working against the dissipative force is not recovered back. Some irreversible process occur in nature such as friction where extra work to cancel the effect of friction. Salt dissolves in water but a salt does not separate by itself into pure salt and pure water.

Q.10. Assertion : Work and heat are two equivalent form of energy.
Reason : Work is the transfer of mechanical energy irrespective of temperature difference, whereas heat is the transfer of thermal energy because of temperature difference only.

Answer Answer: (a) Heat is similar to work in that both represent ways of transferring energy. Neither heat nor work is an intrinsic property of a system, that is, we cannot say that a system contains a certain amount of heat or work.

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