Topic: Electric flux and Gauss's law applications· Electrostatics

If _S E· dS=0 over a surface, then :

1. the electric field inside the surface is necessarily uniform.

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

3. the magnitude of electric field on the surface is constant.

4. all the charges must necessarily be inside the surface.

Doubtly Asked 30 Oct 2026 NEET UG 2023 Practice test neet Save WhatsApp Report

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Answer: 2. the number of flux lines entering the surface must be equal to the number of flux lines leaving it.

\(\oint \vec E\cdot d\vec S = q_{enc}/\varepsilon_0=0\) means the net flux is zero, so the net charge enclosed is zero.

Zero net flux means as many field lines enter the surface as leave it (option 2). It does not say the field is uniform or constant on the surface, nor that all charges are inside. Charges may be absent, or equal and opposite charges may be present inside, or outside charges may exist.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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If _S E· dS=0 over a surface, then :

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