Question

A gas can be taken from $A$ to $B$ via two different processes $ACB$ and $ADB$. When path $ACB$ is used $60\, J$ of heat flows into the system and $30\, J$ of work is done by the system. If path $ADB$ is used work done by the system is $10\, J$. The heat Flow into the system in path $ADB$ is :

• A. 80 J
• B. 20 J
• C. 100 J
• D. 40 J

Answer 1

Answer: (D)

40 J

Answer 2

$\Delta Q_{ACB} = \Delta W_{ACB} + \Delta U_{ACB}$
$\Rightarrow \; 60 J = 30 J + \Delta U_{ACB}$
$\Rightarrow \; \Delta U_{ACB} = 30 \;J$
$\Rightarrow \; \Delta U_{ADB} = \Delta U_{ACB } = 30 \; J$
$\Delta Q_{ACD} = \Delta U_{ACB} + \Delta W_{ADB}$
= $10\, J + 30\, J = 40\, J$