Question

If a gas absorbs 200 J of heat and expands by 500 cm${}^3$ against a constant pressure of $2\times {10}^5$ Nm${}^{-2}$, then the change in internal energy is:

• A. -300 J
• B. -100 J
• C. +100 J
• D. +300 J

Answer 1

Answer: (C)

+100 J

The expression for the change in internal energy is given by,

$\Delta U=q+w$
$q$ $=$ heat absorbed $=$ $200$ J
$w$ $=$ work done $=-P_{x}V$
$=-2\times {10}^5\times 500\times {10}^{-6}$
$=$ $-100$ N - m
$\Delta U=200-100J$$=$ $100$ J

Hence, the correct option is $C$