The P - V diagram of a system undergoing thermodynamic changes is as shown in the figure. The work done by the system in going from `AtoBtoC` is 30 J. If 68 J of heat is given to the system, then the change in the internal energy of the system between A and C is

Options

A. 34 J
B. 38 J
C. 50 J
D. 55 J

Answer

B

Explanation

From the first law of thermodynamics
`dQ=dU+dW" "thereforedU=dQ-dW`
`therefore` The change in internal energy = 68 - 30 = 38 J
The change in the internal energy of a system depends only upon its initial and final states and is independent of the actual path followed. Hence we get the same change i.e. 38 J in U, whether the system goes from `AtoBtoC` or directly from `AtoC`.