Three charges +Q, q, +Q are placed respectively, at distance, 0, d//2 and d from the origin, on the x-axis. If the net force experienced by +Q placed at x=0, is zero, then value of q is :

Options

A. `-Q//2`
B. `-Q//4`
C. `+Q//2`
D. `+Q//4`

Answer

B

Explanation

If net force on `+Q` (at `x=0`) is zero, then
Magnitude of force by q Q (at `x=0`)= Magnitude of force by Q( at x=d) and Q(at x=0) and the directions are exactly opposite so. Q. is -ve.
`implies (kQq)/((d//2)^(2))=((dQ)^(2))/(d^(2))impliesq=-Q/4` i.e. option 2.