Two charge `3 xx 10^(-8)C and -2 xx 10^(-8)C` are located 15 cm apart. At what point on the line joining the two charges the electric potential zero? Take the potential at infinity to be zero.

Explanation

Let P be the required point on the x-axis where the potential is zero. We have

`1/(4pi epsi_(0)) [(3 xx 10^(-8))/(x xx 10^(-2)) -(2 xx 10^(-8))/((15-x) xx 10^(-2))]=0`
where x is in cm. That is `3/x-(2)/(15-x)=0" which gives x=9cm"`
If x lies on the extended line OA, the required condition is `3/x -(2)/(x-15)=0` which gives x=45 cm. The electric potential is zero at 9cm and 45 cm away from the positive charge on the side of the negative charge.