If oint S vec E × dvec S = 0 over a surface, then :

the number of flux lines entering the surface must be equal to the number of flux lines leaving it.

the magnitude of electric field on the surface is constant.

all the charges must necessarily be inside the surface.

the electric field inside the surface is necessarily uniform.

Physics · Electrostatics

NEET (UG) 2023 — Question 9

If $\oint_S \vec{E} \cdot d\vec{S} = 0$ over a surface, then :

Option A:
the magnitude of electric field on the surface is constant.
Option B:
all the charges must necessarily be inside the surface.
Option C:
the electric field inside the surface is necessarily uniform.
Option D:
the number of flux lines entering the surface must be equal to the number of flux lines leaving it.
Correct

Answer: D

Step-by-step solution

Given $\oint_S \vec{E} \cdot d\vec{S} = 0$ . By Gauss's law, $\oint_S \vec{E} \cdot d\vec{S} = \frac{Q_{\text{enc}}}{\epsilon_0}$ . Thus $Q_{\text{enc}} = 0$ , meaning no net charge is enclosed by the surface. Electric field lines originate from positive charges and terminate on negative charges. If the net charge enclosed is zero, the number of field lines entering the surface must equal the number leaving. Hence, option D is correct.

Answer key and solution verified before publishing.

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Exam: NEET (UG) 2023
Paper: 2023 paper
Subject: Physics
Chapter: Electrostatics
Topic: Electric flux and Gauss's Law

Answer: D

Step-by-step solution

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