A closed surface in vacuum encloses charges -q and +3q. Another charge -2q lies out side the surface. The total electric flux over the surface is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 2q/\epsilon_{o} \)
By Gauss’s law the net flux through a closed surface depends only on the charge enclosed by it, \( \phi = q_{\mathrm{enc}}/\epsilon_0 \). A charge outside the surface sends as many field lines in as out, so it adds nothing to the net flux.
\( q_{\mathrm{enc}} = -q + 3q = 2q \)
\( \displaystyle \phi = \frac{2q}{\epsilon_0} \)