A square surface of side `L m` is in the plane of the paper. A uniform electric field `vec(E )(V//m)`, also in the plane of the paper, is limited only to the lower half of the square surface (see figure). The electric flux in `SI` units associated with the surface is:

Options

A. `EL^(2)//(2 epsilon_(0))`
B. `EL^(2)//2`
C. zero
D. `EL^(2)`

Answer

C

Explanation

Electrtic flux `(phi_(e ))` is a measure of the number of field lines crossing a surface. The number of field lines passing through unit area `(N//A)` will be proportional to the electric field, or,
`(N)/(A) prop Eimplies N prop EA`
The quantity `EA` is the electric flux through surface `S`.
In this problem, lines of force that enter the closed surface leave the surface, so no electric flux is bound to the system. Hence, electric flux is zero.