Question

In the P-V diagram shown, the gas does $5J$ of work in isothermal process ab and $4J$ in adiabatic process $bc$. What will be the change in internal energy of the gas in straight path $c$ to $a$?

• A. $9J$
• B. $1J$
• C. $4J$
• D. $5J$

Answer 1

The correct option is C $4J$

In a cyclic process,

change in internal energy is zero.

$\Delta {}_a{U}_a=0=\Delta {}_a{U}_b+\Delta {}_b{U}_c+\Delta {}_c{U}_a$

since process a-b is isothermal;

change in internal energy =0

since process b-c is adiabatic;

$Q=0$

$\therefore \Delta U=-\Delta W=4J$