An electric field →E=4x^i−(y2+1)^jN/C passes through the box shown in figure. The flux of the electric field through surface ABCD and BCGF are marked as ϕ1 and ϕ11 respectively. The difference between (ϕ1−ϕ11) is (in NM2/C)
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Solution
Flux of the electric field →E through any area →A is defined as ϕ=→E⋅→A=EAcosθ
Here, θ= angle between electric field and area vector of a surface
For surface ABCD Angle θ=90∘ ∴ϕ1=∫E.Acos90∘=0
For surface BCGFϕ11=∫→E⋅−→dA ∴ϕ11=[4x^i−(y2+1)^j]⋅4^i=16x=16×3 ϕ11=48Nm2C ∴ϕ1−ϕ11=−48