Question

Two charges `3xx10^(-8) C and -2xx10^(-8)C ` are located 15 cm apart. At what point on the line joining the two charges is the electric potential zero ? Take the potential at infinity to be zero.

Answer 1

Let the location of positive charge be taken as the origin O, Fig and line P be required point, where potential is zero. Let `OP = x cm`

Potential at P is `V = (3xx10^(-8))/(4 pi in_(0) (x xx 10^(-2))) + (-2xx10^(-8))/(4pi in_(0) (15 - x) xx 10^(-2)) = 0`
`:. (3)/(x) - (2)/(15 - x) = 0` , which gives `x = 9 cm`.
If P lies on extented line OA, the condition for zero electric potenitial would be `(3)/(x) - (2)/(x - 15) = 0`,
Which gives `x = 45 cm`
Hence electric potential is zero at 9 cm and 45 away from positive charge on the side of negative charge.
Potential at infinity is taken zero in the formula used.