Electric Flux
Definition, formula, and units of electric flux, representing the number of electric field lines passing through a given surface.
What is Electric Flux?
A measure of the total electric field lines passing through a given surface area.
Key formula / rule: Electric Flux (Uniform Field)
Key points
- Define electric flux.
- Calculate electric flux for uniform and non-uniform electric fields.
- Understand the relationship between electric flux and electric field lines.
- Relate electric flux to enclosed charge using Gauss's Law.
Common exam trap
Confusing flux with electric field strength.
Definitions
- Term
Electric Flux
- Meaning
A measure of the total electric field lines passing through a given surface area.
- Term
Area Vector
- Meaning
A vector whose magnitude is equal to the area of the surface and whose direction is perpendicular to the surface.
Learning objectives
Define electric flux.
Calculate electric flux for uniform and non-uniform electric fields.
Understand the relationship between electric flux and electric field lines.
Relate electric flux to enclosed charge using Gauss's Law.
Formulae
- Name
Electric Flux (Uniform Field)
- Note
θ is the angle between the electric field vector (•) and the normal vector to the surface (A).
- Expression
ΦE = • A = EA cos θ
- Name
Electric Flux (General)
- Note
Integral over the surface S, where dA is the differential area vector.
- Expression
ΦE = ∫_S • dA
- Name
Electric Flux (Gauss's Law)
- Note
For a closed surface, the total flux is proportional to the net charge enclosed.
- Expression
ΦE = Qenclosed / ε0
Prerequisites
Vectors (dot product)
Electric Field
Area Vector
Basic Calculus (Integration)
Common mistakes
Confusing flux with electric field strength.
Incorrectly calculating the angle θ between E and the area vector.
Forgetting to consider the sign of the charge when applying Gauss's Law.
Assuming uniform field and area for all problems without checking.
Keywords
Electric Flux
Electric Field Lines
Surface Integral
Area Vector
Gauss's Law
Enclosed Charge
Electromagnetism
Practice preview
Which of the following factors does NOT affect the electric flux through a given surface?…
medium
What is the SI unit of electric flux?…
easy
An electric field is given by E = (3i + 4j) N/C. Calculate the electric flux through a surface of area 10 m^2 in the XY-plane.…
medium