the shell), and, therefore, equals its value at the surface, which is [ . (b)] Example . Two charges × – C and – × – C are located 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. Solution Let us take the origin O at the location of the positive charge. The line joining the two charges is taken to be the x -axis; the negative charge is taken to be on the right side of the origin (Fig. .
). FIGURE . Let P be the required point on the x -axis where the potential is zero. If x is the x -coordinate of P, obviously x must be positive.
(There is no possibility of potentials due to the two charges adding up to zero for x < .) If x lies between O and A, we have – – – – ( ) ε x x where x is in cm. That is, x x which gives x = cm. If x lies on the extended line OA, the required condition is x x