Thermodynamics MCQs for NEET — Physics Questions with Answers

The NCERT (Physics) text highlights the importance of reversibility: 'But what is the highest efficiency possible for a heat engine working between two reservoirs at temperatures T1 and T2? It turns out that a heat engine based on idealised reversible processes achieves the highest efficiency possible.' This means it sets the theoretical maximum efficiency.

The NCERT (Physics) text states: 'The idealised reversible process is a quasi-static process with no dissipative factors such as friction, viscosity, etc.'

The context states: 'Equilibrium states of a thermodynamic system are described by state variables. The value of a state variable depends only on the particular state, not on the path used to arrive at that state. Examples of state variables are pressure (P ), volume (V ), temperature (T ), and mass (m ). Heat and work are not state variables.'

The context clearly states: 'The Zeroth Law of Thermodynamics led us to the concept of temperature that agrees with our commonsense notion.' and 'We have arrived at the concept of temperature formally via the Zeroth Law.'

The Zeroth Law states: 'two systems in thermal equilibrium with a third system separately are in thermal equilibrium with each other'. This implies that if $T_A = T_C$ and $T_B = T_C$, then $T_A = T_B$, meaning A and B are in thermal equilibrium.

The context defines internal energy: 'Internal energy is simply the sum of the kinetic energies and potential energies of these molecules... Internal energy is thus, the sum of molecular kinetic and potential energies in the frame of reference relative to which the centre of mass of the system is at rest.'

The context mentions: 'Heat flows from the body at a higher temperature to the one at lower temperature. The flow stops when the temperatures equalise; the two bodies are then in thermal equilibrium.'

The text states: 'Internal energy U of a system is an example of a thermodynamic ‘state variable’ – its value depends only on the given state of the system, not on history i.e. not on the ‘path’ taken to arrive at that state.' In another section, it lists 'change in internal energy, ∆U, depends on initial and final states only and is a state function'.

The context states: 'Temperature is a marker of the ‘hotness’ of a body. It determines the direction of flow of heat when two bodies are placed in thermal contact.'

The context states: 'On contact between a hot body and a cold body, the fluid (called caloric) flowed from the colder to the hotter body!'