# Flux
Flux refers to a flow of matter or energy. Examples include water through a pipe, blood through veins, or air over an airplane's wing.

While there's nothing directly *flowing* in an electric field, the term flux is used to describe the total strength of a field.

In the simplest case with a uniform field of magnitude $E$ perpendicular to an area $A$, the flux is described as follows:
$$ \Phi = EA$$
- $E$ refers to the amplitude
- $A$ refers to the area

If the area is tilted relative to the field, then the strength of the field is reduced by a factor of $\cos \theta$, where $\theta$ is the angle between the electric field $\vec{E}$ and a vector $\vec{A}$ that's normal to the surface. This generalizes our flux equation to $\Phi = EA\cos\theta$