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What is Electric Flux? | Maximum & Minimum Flux

June 8, 2022
written by Adeel Abbas

Electric flux measures the electric field that permeates a given surface but the electric field itself cannot flow. This is a method of expressing the intensity of the electric field at an arbitrary distance from the electric charge that creates the electric field. It has many applications in different fields.

 The electric field E can exert a force on the charge at any point in space.

Download the pdf notes of electric flux Class 12 Physics

What is Electric Flux?

A total number of electric field lines passing through a vector area is called electric flux or “The scalar product of electric intensity E and vector area A”.

What is the Vector area?

It is an area whose magnitude is equal to the surface area A of the element but its direction is normal to this area.

Electric Flux Formula

Electric flux is denoted by the Greek letter Ø.



θ is the angel between field lines and normal to the area

Unit of electric flux


Electric flux depends on

  • Electric intensity
  • Vector area

Maximum Electric flux

 When the area is held perpendicular to the field lines having uniform electric field intensity E then electric flux, in this case, is given as

image showing the maximum electric flux


θ=0 so

Ø =EAcos0

As cos0=1


The area is held perpendicular to the electric field lines. It is the maximum flux.

Minimum Electric flux

When area A has been placed parallel to the field lines, in this case, no line in this area so flux, in this case, is given as

image of minimum electric flux


θ=90 so

Ø =EAcos 90

As cos90=0


A is held parallel to the field lines. In this flux is zero.

Flux at Angle θ

When A is inclined at an angle θ with the lines then we will take the projection of the area which is perpendicular to the field lines. The area of projection, in this case, is equal to Acosθ, thus flux is given as

image showing the electric flux at some angle

Ø=EAcos θ

θ is the angel between field lines and normal to the area


Frequently Asked Questions – FAQs

What are electric flux and its unit?

Electric flux is defined as a measure of the number of field lines that cross a surface. Electric flux ϕ=EAcosθ. The unit of electric flux is Nm2C-1.

What is an electric field?

An electric field is a physical field that surrounds an electrically activated particle or object. It exerts a force (repulsion or attraction) on other charged particles or objects in the field. In other words, it can be defined as the physical field of the body of a charged particle.

What is the SI unit of flux?

The SI unit of magnetic flux is the Weber (Wb).

Can flux be negative?

Negative Flux is when there is more inward flow of field lines than outward flow. The magnitude of the flux is still the same, it’s just that the direction has changed. Flux is the act of flowing in or flowing out.
So, for example, if the lines of force are directed inward on a surface, this would be classified as negative Flux.