Two point charges -q and +q are located at points (0, 0, -a) and (0, 0, +a) respectively. The electric potential of a point (0, b, 0), where b > a, is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Zero
The potential at a point is the algebraic sum of the potentials of the individual charges. The point \( (0, b, 0) \) is at the same distance from both charges, since each is a distance a from the origin along the z axis.
\( r = \sqrt{b^{2} + a^{2}} \)
\( \displaystyle V = \frac{1}{4\pi\epsilon_0}\left[\frac{+q}{r} + \frac{-q}{r}\right] = 0 \)
Shortcut: The two charges form a dipole along the z axis, and the plane \( z = 0 \) (which contains the point \( (0, b, 0) \)) is the equatorial plane of that dipole. The potential on the equatorial plane of a dipole is zero at every point, whatever b is.