NCERT Solutions for Class 11 Physics Ch-11: Thermodynamics

Answer: The first law of thermodynamics states that the heat supplied to a system (Q) is equal to the sum of the increase in internal energy of the system (ΔU) and the work done by the system on its surroundings (W): Q = ΔU + W. It represents the principle of conservation of energy applied to thermodynamic systems.

Answer: An isothermal process occurs at constant temperature, with the system in continuous thermal contact with a reservoir so that ΔU = 0 and Q = W. An adiabatic process occurs with no heat exchange between the system and surroundings (Q = 0), so any work done results directly in a change of internal energy, W = −ΔU.

Answer: The Kelvin-Planck statement of the second law of thermodynamics states that it is impossible to construct a device that, operating in a cycle, produces no effect other than the extraction of heat from a single reservoir and its complete conversion into an equivalent amount of work.

Answer: A Carnot engine is an ideal, reversible heat engine that operates between two temperature reservoirs using the Carnot cycle, consisting of two isothermal and two adiabatic processes. Its efficiency is given by η = 1 − (T2/T1), where T1 and T2 are the absolute temperatures of the hot source and cold sink respectively; it represents the maximum possible efficiency for any heat engine operating between those two temperatures.

Answer: A refrigerator is a device that operates in a cycle to transfer heat from a colder body (inside the refrigerator) to a hotter body (the surroundings), using external work input, effectively acting as a reverse heat engine.