Consider a point charge +q placed at the origin and another point charge -2p 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 at a distance x from the charge +q as shown in the figure
The toatal electric potential at P is zero.

`V_("tot")=(1)/(4piepsilon_(0))((q)/(x)-(2q)/((9-x)))=0`
which gives `(q)/(x) =(2q)/((9-x))` or `(1)/(x)=(2)/((9-x))`
Hence x =3 n