Q.

Consider an electric field E→=E0x^ where E0 is a constant. The flux through the shaded area (as shown in the figure) due to this field is             [2011]

1 2E0a2  
2 2E0a2  
3 E0a2  
4 E0a22  

Ans.

(3)

Given E→=E0 x^

i.e., the electric field E→ acts along the +x-direction and is constant.

Therefore, the electric flux through the shaded portion whose area  A→=a×2a=2a2 is

ϕ=E→·A→=EAcosθ=E0(2a2)cos45°=E0(2a2)×(12)=E0a2           (∵ angle between E→ and A→,Q=45°)