Two point charges ` + 4 muC and -2 muC` are separated by a distance of 1 m in air. Calculate at what point on the line joining the two charges is the electric potential zero.

Explanation

Here `q_1 = 4 mu C , q_2 = -2 muC ` and distance between them r = 1 m

As shown in figure net electric potential is zero at point `C_1` situated between the two charges and at point `C_2` situated on extension of line joining the two charges. If distance of point `C_1 or C_2` from `q_1` be x, then
For point `C_1 : V_1 + V_2 = 1/(4pi epsi_0) [q_1/x+ q_2/((r - x))] = 0 rArr (4muC)/x + ((-2 muC))/((1-x)) = 0 rArr x = 2/3 m`
Similarly for point `C_2 : q_1/x + 1/((x -r)) = 0 rArr (4 muC)/x + ((-2 muC))/((x + 1)) = 0 rArr x = 2m`