Question

When the state of a gas adiabatically changed from an equilibrium state A to another equilibrium state B, an amount of work done on the system is 35 J. If the gas is taken from state A to B via process in which the net heat absorbed by the system is 12 cal, then the net work done by the system is (1 cal = 4.19 J)

• A. 13.2 J
• B. 15.4 J
• C. 12.6 J
• D. 16.8 J

Answer 1

Answer: (B)

15.4 J

Answer 2

: In the first – case adiabatic change,

$\Delta Q = 0 , \Delta W = - 35 j$

Form $1 ^ { s t }$law of thermodynamics

$\Delta Q = \Delta U + \Delta W$ …. (i)

Or $0 = \Delta U - 35$

$\therefore \Delta U = 35 j$

In the second case

$\Delta Q = 12 \mathrm { cal } = 12 \times 4.2 \mathrm {~J} = 50.4 \mathrm {~J}$

using (i)