Two charges $\pm 10 \mu C$ are placed $5.0 ext{ mm}$ apart. What is the approximate electric field

Question

Two charges $\pm 10 \mu C$  are placed $5.0	ext{ mm}$ apart. What is the approximate electric field at a point $Q$, $15	ext{ cm}$ away from the centre $O$ on a line passing through $O$ and normal to the axis of the dipole?

Professor PC Thomas Classes · Answer

For an equatorial point with $r \gg a$, $E \approx \frac{1}{4\pi\epsilon_0} \frac{p}{r^3} = 9 	imes 10^9 	imes \frac{5 	imes 10^{-8}}{(0.15)^3} = 1.33 	imes 10^5	ext{ N/C}$.