Question

two fixed point charges +4eand +e units are separated by a distance a.where should a third point charge for it to be equilibrium?​

Answer 1

Correct option is

A

32a

The third charge q is in equilibrium only when 

force on it due to +4e= force due to +e

i.e  x2k(4e)q=(a−x)2k(e)q

or 4(a−x)2=x2

or 2(a−x)=x

or 2a−2x=x⇒x=32a

Answer 2

Explanation:

Two fixed point charges + 4e and + e units are separated by a distance a. Where should the third point charge be placed for it to be in equilibrium? Hence the charge q should be held at a distance 2a / 3 from charge (+ 4e).