Question

When is the electric field at point P zero?
1. +q------r------P------r------+q

2. 4q------2r------P----r----q

3. -4q-------r------q----r----P

4. -q------r------P------r------+q
here r is the distance between the charges.

Answer 1

Option(4)
Electric field gets cancelled by equal and opposite charges placed at equal distance rates. Net electric field at P,
Enet=E due to - q+E due to +q
=k*-q/r^2+k*q/r^2
=0