Quantity of electric charge

Electricity and Magnetism Level 2

In the above diagram, find the quantity of the electric charge $Q$ in the capacitor when the switch has been closed for a long time.

20 \mu C

30 \mu C

3 \mu C

2 \mu C

1 solution

Pranjal Jain
Oct 8, 2014

Diagram Diagram

Assume potential at C be 0V. Now potential at B and D will be 11V and 17V respectively.

Apply Kirchoff's current law at point A to find voltage. (You may also use Kirchoff's voltage law!)

Let potential at A be V $\frac{V-17}{4}+\frac{V-11}{2}+\frac{V}{3}=0 \implies V=9V$

Now potential difference between plates of capacitor=11-9=2V

$q=CV \implies q=10 \times 2=20$ microcoulombs