Explain the concept of electric flux.

1. Introduction

Electric flux is an important concept in electrostatics which describes the total number of electric field lines passing through a given surface. It helps us understand how electric fields interact with surfaces.

2. Definition

Electric flux through a surface is defined as the surface integral of the electric field over that surface. It represents the total electric field passing normally through the surface.

Φ = E · A cosθ

3. SI Unit

The SI unit of electric flux is:

N m² / C (Newton meter squared per Coulomb)

4. Physical Meaning

Electric flux gives the measure of how many electric field lines pass through a surface. If the surface is perpendicular to the electric field, flux is maximum. If the surface is parallel, flux is zero.

5. Dependence of Electric Flux

• Depends on magnitude of electric field (E)
• Depends on area of surface (A)
• Depends on angle between field and surface normal (θ)

6. Special Cases

If θ = 0° (surface perpendicular to field):

Φ = EA

If θ = 90° (surface parallel to field):

Φ = 0

7. Relation with Gauss Law

Electric flux plays a key role in Gauss’s law which states that total electric flux through a closed surface is equal to the charge enclosed divided by permittivity of free space.

Φ = Q / ε₀

8. Important Points

• Electric flux can be positive, negative or zero
• It depends on orientation of surface
• It is a scalar quantity

Final Result (To Remember)

Φ = E A cosθ

Φ = Q / ε₀ (for closed surface)

Electric flux represents total electric field passing through a surface.