A small plane area is rotated in an electric field. The flux of electric field through the area is maximum when
A
Electric field lines are parallel to the surface
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B
Electric field lines are perpendicular to the surface
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C
Electric field lines are at 60∘ to the surface
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D
Electric field lines are at 45∘ to the surface.
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Solution
The correct option is B Electric field lines are perpendicular to the surface
We know that electric flux (ϕ) through a plane area is given by ϕ=→E.→A=EAcosθ
It will be maximum when cosθ=1 or θ=0∘.
Thus, area vector and electric field are in the same direction.
Hence, electric field lines are perpendicular to the surface.