If the amounts of electric fluxes entering and leaving an enclosed surface are φ1 and φ2, respectively, then the electric charge inside the surface will be
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (φ2 − φ1)ε0
By Gauss’s law, the net electric flux out of a closed surface is \( q/\varepsilon_0 \). Flux leaving the surface counts as positive and flux entering counts as negative.
\( \displaystyle \phi_{\mathrm{net}} = \phi_2 - \phi_1 = \frac{q}{\varepsilon_0} \)
\( \displaystyle q = (\phi_2 - \phi_1)\varepsilon_0 \)
Note: This question is from NCERT (2026-27). NTA sets numerical questions from NCERT too, so do not ignore NCERT while practising numericals.
NCERT (2026-27):
Gauss’s Law – “… Equation (1.30) is a simple illustration of a general result of electrostatics called Gauss’s law.
We state Gauss’s law without proof:
Electric flux through a closed surface S
\( \displaystyle = q/\varepsilon_0 \qquad (1.31) \)
q = total charge enclosed by S.”