Question

two point charges + q and + 4 Q are separated by a distance 6a find the point joining the two charges where the electric field is zero​

Answer 1

The electric fiels is zero at P only , if the field due to +Q balance the field due to +4Q

$\frac{1}{4\pi ∈0} . \frac{Q}{x^{2} } =\frac{1}{4\pi ∈0}.\frac{4q}{(6a-x)^{2} }$

1x2=4(6a−x)2

Taking square root or both sides.

$\frac{1}{x^{2} } = \frac{4}{(6a-x)^{2} }$

On cross multiplying we get,

$2a = 6a-x$

$x = 2a$

Hence the required point is at a distance of 2a from Q