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

A the electric field inside the surface is necessarily uniform.

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

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

D all the charges must necessarily be inside the surface.

The answer is B.

Solution

Zero net flux means flux entering equals flux leaving.

$\oint\vec{E}\cdot d\vec{S}=0\Rightarrow\phi_{net}=\phi_{in}-\phi_{out}=0\Rightarrow\phi_{in}=\phi_{out}$

Concept zero net flux

42 questions from this chapter have appeared across 23 exam years.