Consider a point charge +q placed at the origin and another point charge -2q placed at a distance of 9 m from the charge +q. Determine the point between the two charges at which electric potential is zero.

Explanation

According to the superposition principle, the total electric potential at a point is equal to the sum of the potentials due to each charge at that point.
Consider the point at which the total potential zero is located at a distance x from the charge +q as shown in the figure.

The total electric potential at P is zero.
`V_("tot") = (1)/(4pi epsilon_(o) ) ( (q)/(x) - (2q)/( (9-x) ) )= 0`
which gives `(q)/(x) = (2q)/( (9-x))`
or `(1)/(x) = (2)/( (9-x))`
Hence, ` x= 3`m