Home / Topics / Electrostatics
Electric flux
Intermediate
Field lines through a surface.
Φ = ∮E·dAFlux Φ = ∮E·dA counts the field lines passing through a surface. For a uniform field through a flat area, Φ = EA cosθ.
1000 N/C through 0.5 m² face-on: 500 N·m²/C.
Flux is a scalar and can be negative.
In more detail
Electric flux is the number of field lines passing through a surface, Φ = E·A for a uniform field perpendicular to the surface. It is a measure of the field passing through a given area.
Real-world uses
- Gauss's law uses flux to find fields in symmetric charge arrangements.
- Engineers use flux calculations in designing shielding.
- Engineers use electric flux to measure how much field passes through a sensor or a detector surface.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
What are the units of flux?
Newton metres squared per coulomb.
Does flux depend on the surface orientation?
Yes, it depends on the angle between the field and the surface normal.
Is flux a vector?
Flux is a scalar obtained by taking the dot product of the field with the area vector.
Related topics in Electrostatics
Field of a dipole · Torque on a dipole in a field · Potential energy of a dipole · Gauss's law · Field of infinite line charge · Field of infinite plane sheet