Consider a closed surface S in a non−uniform electric field (Figure).

Consider a very small area “ds” on this surface. The direction of ds is drawn normal to the surface outward. The electric field over ds is supposed to be a constant E^{→} * E^{→ }and ds^{→ }make an angle θ with each other.

The **electric flux** is defined as the total number of electric lines of force, crossing through the given area. The electric flux dφ through the area ds is,

**dφ = E ds = E ds cosθ**

The total flux through the closed surface S is obtained by integrating the above equation over the surface, φ = ϐ dφ = ϐ E. ds

The circle on the integral indicates that the integration is to be taken over the closed surface. The electric flux is a scalar quantity.

**Its unit is N m ^{2} C^{-1}.**