An isolated sphere has a capacitance of 50 pF. (a) Calculate its radius. (b) how much charge should be placed on it to raise its potential ot `10^4 V`?

Explanation

(a) The capacitane of an isolated sphere is `
`C 4pi epsilon_o R`
`. Thus, `
`50 X 10^(-12) F =(R )/(9 X10^9 mF^(-1)`
` or, `
`R = 50 X 10^(-12) X9 X 10 ^9 m = 45 cm`
`. (b) `
`Q = CV = 50 X10 ^(-12) F X 10 ^4 V = 0.05 muC` .