Q.An electric dipole has a dipole moment of $5\times 10^{-9}\ \text{C}\,\text{m}$. Find the potential at a point on its axial line, $25\ \text{cm}$ from the centre of the dipole.

For a dipole of moment $p=q(2a)$, far-field potential at angle $\theta$ from the dipole axis: $V=kp\cos\theta/r^2$ (for $r\gg a$), derived via scalar superposition of the two point charges with the approximations $r_2-r_1\approx 2a\cos\theta$ and $r_1r_2\approx r^2$. Axial line ($\theta=0$): $V=kp/r^2$, maximum magnitude. Equatorial line ($\theta=90^\circ$): $V=0$ EXACTLY at every point, since equatorial points are equidistant from $+q$ and $-q$ -- unlike the field, which is nonzero (only smaller) there. Falls off as $1/r^2$, one power faster than a point charge's $1/r$, since the dipole's net charge is zero.