Q. If the amount of heat given to a system is $35\ J$ and the amount of work done on the system is $15\ J$, then the change in internal energy of the system is
A) $- 50J$
B) $20J$
C) $30J$
D) $50J$
Explanation
(d) According to first law of thermodynamics
$\mathrm{\Delta}Q = \mathrm{\Delta}U + \mathrm{\Delta}W$
$\mathrm{\Delta}U = \mathrm{\Delta}Q - \mathrm{\Delta}W$
Here $\mathrm{\Delta}Q = 35J,\ \mathrm{\Delta}W = - 15J$
$\therefore\ \mathrm{\Delta}U = 35J - ( - 15J) = 50J$
Note : $\mathrm{\Delta}W$ is negative because work is done on the system
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.