Two point charges `+3 muC` and `+8muC` repel each other with a force of `40 N`. If a charge of `-5 muC` is added to each of them, then the force between them will become

Options

A. `-10N`
B. `+10N`
C. `+20N`
D. `-20N`

Answer

A

Explanation

`F_1=40 N`
`(K(3xx8)xx10^(-12))/(r^2) = 40 N" "...(i)`
`(-K(2xx3) xx10^(-12))/r^2 = F_2 " "...(ii)`
`-(3xx8)/((2xx3)) =40/(F_2)implies F_2=(-40 xx6)/24 = -10N`