Thermodynamics MCQs for NEET — Physics Questions with Answers

The text mentions: 'A most natural explanation of the observations was that heat was a form of energy and the experiment demonstrated conversion of energy from one form to another–from work to heat.' It also noted that 'the amount of heat produced depended on the work done... but not on the sharpness of the drill' contradicting the caloric theory.

The context states: 'Thus, it includes only the (disordered) energy associated with the random motion of molecules of the system.'

The context asks: 'how to assign numerical values to temperatures of different bodies ? In other words, how do we construct a scale of temperature ? Thermometry deals with this basic question...'

The context states: 'The distinction between mechanics and thermodynamics is worth bearing in mind. In mechanics, our interest is in the motion of particles or bodies under the action of forces and torques. Thermodynamics is not concerned with the motion of the system as a whole. It is concerned with the internal macroscopic state of the body.'

The Second Law of Thermodynamics states that many conceivable processes that are perfectly allowed by the First Law are never observed. The example given in the NCERT text is: 'A book lying on a table jumping to a height by itself. But such a thing would be possible if the principle of conservation of energy were the only restriction. The table could cool spontaneously, converting some of its internal energy into an equal amount of mechanical energy of the book... But this never happens.' This illustrates that while energy conservation allows it, the Second Law forbids such spontaneous, ordered energy conversion from a colder object to mechanical work.

The Kelvin-Planck statement explicitly says: 'No process is possible whose sole result is the absorption of heat from a reservoir and the complete conversion of the heat into work.' This implies that a heat engine can never have an efficiency of unity (100%).

The Clausius statement explicitly states: 'No process is possible whose sole result is the transfer of heat from a colder object to a hotter object.' This means that heat naturally flows from hot to cold, and to reverse this flow (as in a refrigerator), external work must be done.

The NCERT text states: 'It can be proved that the two statements above are completely equivalent.'

The NCERT text explicitly states: 'In simple terms, it says that efficiency of a heat engine can never be unity. For a refrigerator, the Second Law says that the co-efficient of performance can never be infinite.'

The NCERT summary states: 'Spontaneous processes of nature are irreversible. The idealised reversible process is a quasi-static process with no dissipative factors such as friction, viscosity, etc.' Therefore, spontaneous processes are typically irreversible and associated with dissipative factors.