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NEET 2023 Phase 1 · PhysicsGauss fluxPrevious Year Question

If ∮ₛ E · dS = 0 over a closed surface, then:

Answer: (A) the number of flux lines entering the surface must be equal to the number of flux lines leaving it.. Answer: (a) Solution: By Gauss's law, the net flux through a closed surface equals q_enclosed/ε₀.

  1. A.the number of flux lines entering the surface must be equal to the number of flux lines leaving it.✓
  2. B.the magnitude of electric field on the surface is constant.
  3. C.all the charges must necessarily be inside the surface.
  4. D.the electric field inside the surface is necessarily uniform.

Correct Answer

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

Solution & Explanation

Answer: (a) Solution: By Gauss's law, the net flux through a closed surface equals q_enclosed/ε₀. If ∮ E · dS = 0, the net enclosed charge is zero, so the net flux is zero. Zero net flux means the total outward flux equals the total inward flux — i.e., the number of field (flux) lines entering the surface equals the number leaving it. This does not require the field to be constant or uniform, nor does it say anything about whether charges lie inside. Hence option (a) is correct.

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