Question

A charge of `-2 C` is at the origin. How much energy would be applied to or released from a `4 C` charge if it is moved from `(-5 ,1 )` to `(3 ,-9 )`?

Answer 1

Initial distance between the `-2C` charge and `4C` charge is `sqrt((-5)^2+(1)^2)m` or, `5.099 m`

And,final distance is `sqrt((3)^2+(-9)^2) m` i.e `9.486m`

That means,distance has been increased in this process,against an attractive force between a negative charge and a positive charge,so energy has to be applied for moving against the attractive force.,and the value is `-U2 -(-U1)` (where, `-U2` is the final energy and `-U1` is the initial energy of the charge)

`9*10^9*(-2)* 4* (1/9.486 - 1/5.099) J` or, `6.552 * 10^9 J`