Question

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

• A. $1 0 0 \, \mu \text{J}$
• B. $- 1 0 0 \, \mu \text{J}$
• C. $8 0 \, \mu \text{J}$
• D. $- 8 0 \, \mu \text{J}$

Answer 1

Answer: (C)

Before the switch S is closed
$\text{Q}_{\text{i}} = \text{C}_{\text{eq}} \text{V}$
$= 5 \times 4 = 2 0 \, \mu \text{C}$
When the switch S is closed
$\text{Q}_{\text{f}} = \text{CV}$
$= 1 0 \times 4 = 4 0 \, \mu \text{C}$
$\mathrm{W}($ cell $)=\Delta \mathrm{QE}=\left(\mathrm{Q}_{\mathrm{f}}-\mathrm{Q}_{\mathrm{i}}\right) \times \mathrm{E}$
$= 2 0 \times 4 = 8 0 \, \mu \text{J}$