Question

Internal energy of a system is defined as?

(a) The sum of kinetic energies of all molecules of the system

(b) The sum of kinetic and potential energies of all molecules of the system

(c) The sum of potential energies of the system

(d) The average kinetic energy of all molecules

The question was asked during an interview.

This is a very interesting question from Thermodynamics in division Thermodynamics of Physics – Class 11

Answer 1

The correct option is (b) The sum of kinetic and potential energies of all molecules of the system

Explanation: The internal energy of a system corresponds to the energy possessed by all molecules. Thus it is the sum of kinetic and potential energies of all molecules in the system considered. Also note that potential energy is frame dependent, so we choose a frame in which the centre of mass is at rest.