Question

A body has 15J of heat energy in a particular state. At the same state it has an internal energy of 30J. Assume no work is done, what will happen to the internal energy if 5J of heat is added to the system?

(a) Heat energy = 20J, Internal energy = 35J

(b) Heat energy = 15J, Internal energy = 30J

(c) Heat energy = 15J, Internal energy = 35J

(d) A body cannot have heat energy in a particular state

I had been asked this question in an international level competition.

Question is taken from Thermodynamics in division Thermodynamics of Physics – Class 11

Answer 1

Correct answer is (d) A body cannot have heat energy in a particular state

Easiest explanation: Heat energy is the energy in transit. A system’s state cannot be defined by heat energy, it is defined by internal energy. Heat and work are path functions. Heat can be supplied or removed from a system but can’t define a system in a state.