 Flux

A flux records transport of a quantity through a surface per unit time. A flux density $\mathbf{j}$ gives total transport rate ${\int }_S\mathbf{j}\cdot \mathbf{n}dS$, where $\mathbf{n}$ is the unit normal vector. A conservation law relates its divergence to the local change in the quantity's density.

Flux can refer to several different concepts depending on the context. Here are some of the most common interpretations: 1. **Physics and Engineering**: In physics, "flux" often refers to the rate of flow of a physical quantity through a surface. For instance, electromagnetic flux refers to the amount of electromagnetic field passing through a given area, while magnetic flux refers to the amount of magnetic field.