A parallel plate capacitor `(C=-400 pF)` is charged to `1000V`. (a) find energy strored in capacitor. (b) find new potential difference if separation between plates is doubled.

Explanation

(a) `U=(1)/(20)CV^(-2)=(1)/(2)xx400xx10^(-12)xx(1000)^(2)`
`=2000xx10^(-6)J=200muJ`
(b) Since charge remains same
`Q=CV=C'V'`
`C=(Ain_(0))/(d),.C'=(Ain_(0))/(2d)=(c)/(2)`
`CV=(c)/(2)V'impliesV'=2V=2xx1000=2000V`