Question

A gas is at constant pressure $4 \times 10^{5} N / m ^{2}$. When a heat energy of $2000\, J$ is supplied to the gas, its volume changes by $3 \times 10^{-3} m ^{3}$. What is the increase in its internal energy?

• A. 650 J
• B. 900 J
• C. 800 J
• D. 400 J

Answer 1

Answer: (C)

Given, pressure, $p=4 \times 10^{5} N / m ^{2}, \Delta Q=2000\, J$
Change in volume, $\Delta V=3 \times 10^{-3} m ^{3}$
Now, the work done to change volume is
$\Delta W=p \Delta V=4 \times 10^{5} \times 3 \times 10^{-3}$
$=12 \times 10^{2}=1200\, J$
According to first law of thermodynamics,
So, change in internal energy,
$\Delta U=\Delta Q-\Delta W=2000-1200=800\, J$