Electric Flux. The number of field lines passing through an element of an area is known as electric flux through that area.

It is denoted by .

Its SI unit is Nm2C-1.

When an area is held perpendicularly against the electric field lines, the electric flux is maximum.

But when an area is held parallel to the electric field lines, no lines pass through that area and the it is zero/minimum.

Flux is calculated by

=EAcos

A denotes the area and E is the uniform electric field intensity.

is the angle between the field lines and the normal to the area.

Electric flux is a scalar product.

Through A Surface Enclosing A Charge

Let’s assume that a sphere has a charge q placed at the center of itself.

Now, according to the formula, =E.A  , for the computation of electric flux, the surface should be flat.

Since the surface is not flat, we will divide the area of the surface into small patches of A1, A2, A3, and so on.

So for the total flux, =EA1. EA2. E.A3.

As E= 14qr2

=14qr2 (total surface area)

Total surface area of a sphere is 4 r2

Now we will put the whole formula.

=14qr2 4 r2

4 will be canceled out.

And r2 will be canceled out.

The end product is, =q

This is the formula for calculating electric flux through a surface enclosing a charge.