Q. When an ideal gas in a cylinder was compressed isothermally by a piston, the work done on the gas was found to be $1.5 \times 10^{4}\ joules$. During this process about
A) $3.6 \times 10^{3}\ cal$ of heat flowed out from the gas
B) $3.6 \times 10^{3}\ cal$ of heat flowed into the gas
C) $1.5 \times 10^{4}\ cal$ of heat flowed into the gas
D) $1.5 \times 10^{4}\ cal$ of heat flowed out from the gas
Explanation
(a) In isothermal compression, there is always an increase of heat which must flow out of the gas
$\mathrm{\Delta}Q = \mathrm{\Delta}U + \mathrm{\Delta}W \Rightarrow \mathrm{\Delta}Q = \mathrm{\Delta}W\ \lbrack\because\mathrm{\Delta}U = 0\rbrack$
$\Rightarrow \ \mathrm{\Delta}Q = - 1.5 \times 10^{4}J = \frac{1.5 \times 10^{4}}{4.18}cal = - 3.6 \times 10^{3}cal$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.