Question

A charge of `-1 C` is at the origin. How much energy would be applied to or released from a `-1 C` charge if it is moved from `(-7 ,1 )` to `(-1 ,4 )`?

Answer 1

Initial distance between the two charges is `sqrt((-7)^2 + (1)^2)` or `7.07m` and final distance is `sqrt((-1)^2 + (4)^2)` i.e `4.12m`

So, initial potential energy of the system is `(U1) = 9*10^9*(-1)*(-1)/7.07 J` and final potential energy `(U2) = 9*10^9*(-1)*(-1)/4.12 J`

Clearly, `U1` is smaller than `U2`

So, energy that has to be added is `U2-U1` = `9.1 * 10^8 J`