Calculate the capacity of unknown capacitance is connected acrosss a battery of V volts. The charge stored in it is `360 muC`. When potential across the capacitor is reduced by 120V, the charge stored in it becomes `120 muC`.
Calculate (i) the potential V and unknown capacitance C. (ii) What will be the charge stored in the capacitor. If the voltage applied had increased by 120 V

Explanation

From the relation `Q=CV=360 mu C`
When potential is reduced to 120V
`120 mu C= C( V-120) = 120 C`
`rArr" " 120 mu C = 360 mu C- 120 C rArr " "120=240 mu C`
`rArr C=(cancel (240)muC)/cancel (120)=2 mu F`
Potential `V= (360 mu C)/(2 mu F) = 180 V`
Charged stored when voltage applied is increased by `120V Q ^(1)=2 mu F xx (180V + 120 V) = 600 mu C`