Question

In the given figure the work done by the battery after the switch $S$ is closed is

• A. $100\mu \text{J}$
• B. $-100\mu \text{J}$
• C. $80\mu \text{J}$
• D. $-80\mu \text{J}$

Answer 1

Answer: (C)

Before the switch S is closed
${\text{Q}}_{\text{i}}={\text{C}}_{\text{eq}}\text{V}$
$=5\times 4=20\mu \text{C}$
When the switch S is closed
${\text{Q}}_{\text{f}}=\text{CV}$
$=10\times 4=40\mu \text{C}$
$\mathrm{W}($ cell $)=\Delta \mathrm{QE}=\left({\mathrm{Q}}_{\mathrm{f}}-{\mathrm{Q}}_{\mathrm{i}}\right)\times \mathrm{E}$
$=20\times 4=80\mu \text{J}$