Two balls with charges `5 muC` and `10m C` are at a distance of `90m` from each other. In order to reduce the distance between them to `45m`, the amount of work to be performed in joule is :

Answer

5

Explanation

Here, `q_(1) = 5 mu C = 5xx10^(-6) C`
`q_(2) = 10m C = 10xx10^(-3) C`
`r_(1) = 90m, r_(2) = 45m, W = ?`
`W = U_(2) - U_(1) = (q_(1) q_(2))/(4pi in_(0) r_(2)) - (q_(1) q_(2))/(4pi in_(0) r_(1))`
`= (q_(1) q_(2))/(4pi in_(0)) [(1)/(r_(2)) - (1)/(r_(1))]`
`(5xx10^(-6))xx(10xx10^(-3)) xx9xx10^(9) [(1)/(45) - (1)/(90)]`
`W = 450xx (1)/(90) = 5 J`