Question

A capacitor of unknown capacitance is connected across a battery of V volts. The charge stored in it is 360 µC. When potential across the capacitor is reduced by 120 V, the charge stored in it becomes 120 µC. Calculate:

(i) The potential V and the unknown capacitance C.

(ii) What will be the charge stored in the capacitor, if the voltage applied had increased by 120 V?

Answer 1

(i)

If unknown capacitor of capacitance ‘C’ is connected to a battery of ‘V’ volts,

Q = CV

⇒ CV= 360 µC ....(i)

On reducing the potential/voltage by 120 V

So, Q′=C(V–120)

⇒ C (V– 120) = 120 µC ....(ii)

On solving equation (i) and (ii)

Unknown capacitance from equation (i)

Q = CV

(ii) Charge on the capacitor, if voltage is increased by 120 V