Question

A perfect gas goes from state $A$ to state $B$ by absorbing $8\times {10}^5$ joule and doing $6.5\times {10}^5$ joule of external work. If it is taken from same initial state $A$ to final state $B$ in another process in which it absorbed ${10}^{5}J$ heat, then in the second process work done ?

• A. On gas is ${10}^{5}J$
• B. On gas is $0.5\times {10}^{5}J$
• C. By gas is ${10}^{5}J$
• D. By gas is $0.5\times {10}^{5}J$

Answer 1

The correct option is B On gas is $0.5\times {10}^{5}J$

solution :

$\Delta Q=\Delta U+\Delta W$

$8\times {10}^5=\Delta U+6.5\times {10}^5$

$\Delta U=1.5\times {10}^{5}J$

by process 2

$\Delta Q=\Delta U+\Delta W$

${10}^5=1.5\times {10}^5+\Delta W$

$\Delta W=-0.5\times {10}^{5}J$

and it is negative means work is done on the gas

hence the correct opt: B