JEE Class main Answered
Every substance possesses a definite amount of energy which depends on factors such as chemical nature, temperature and pressure.
This energy is called the internal energy of the system. It is represented by U.
The internal energy U of the system may change when:
Heat passes into or out of the system
Work is done on or by the system
DU = UB−UA
UB= internal energy of the system in State B
UA= internal energy of the system in State AInternal energy of a system cannot be measured directly, but can determine the change in internal energy (ΔU)