Q.

If ∮E→·dS→=0 over a surface, then                   [2023]

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

Ans.

(3)

The term ∮E→·ds→ represents electric flux over the closed surface and electric flux is proportional to the number of electric field lines. If ∮E→·ds→=0, it means that the number of flux lines entering the surface must be equal to the number of flux lines leaving it.