Question

For the gas shown in the diagram, 70 J of energy is added to the system.Where is the heat added to the system?

• A. $A\to B$
• B. $B\to C$
• C. $C\to D$
• D. $D\to A$
• E. $A\to B\to C\to D\to A$

Answer 1

The correct option is A $A\to B$

Process AB is an isothermal process i.e $\Delta T_{AB}=0$ or $\Delta U_{AB}=0$

From figure, Volume of the gas expands during process AB, thus $W_{AB}>0$

Using 1st law of thermodynamics, $Q_{AB}=\Delta U_{AB}+W_{AB}$

$\therefore$ $Q_{AB}=0+W_{AB}$ $⟹Q_{AB}=W_{AB}>0$

Thus heat is added to the system during process $A\to B$.