Question

how to find potential difference between two charges​

Answer 1

find the potential at each point (say, A and B) due to individual charges..

at A:

V1 = V due to "Q" = KQ/a

V2 = V due to "-Q" = K(-Q)/√(a^2+4a^2) = -KQ/(√5 a)

so, V at A = V1 + V2 ....

similarly do for point B....

then ,

find the value of | (V at A) - (V at B)|

you will get the answer (using some mathematical tools)...