Energy flux

Definition

Energy flux is the rate of energy transfer per unit area perpendicular to the direction of propagation of an electromagnetic wave. It is measured in watts per square meter (W/m²).

5 Must Know Facts For Your Next Test

1. Energy flux quantifies how much energy passes through a given area in a specific amount of time.
2. It can be calculated using the Poynting vector, which represents the directional energy flux density.
3. The formula for energy flux using the Poynting vector is $S = E \times H$, where $E$ is the electric field and $H$ is the magnetic field.
4. In free space, the magnitude of the Poynting vector can also be expressed as $S = \frac{E^2}{c\mu_0}$, where $c$ is the speed of light and $\mu_0$ is the permeability of free space.
5. Energy flux is crucial in understanding how electromagnetic waves transport energy through different media.

Review Questions

• What are the units used to measure energy flux?
• How do you calculate energy flux using the Poynting vector?
• Why is energy flux important in understanding electromagnetic wave propagation?

Related terms

Poynting Vector: A vector that represents the directional energy flux (the rate of energy transfer per unit area) of an electromagnetic field.

Electromagnetic Wave: A wave composed of oscillating electric and magnetic fields that propagates through space at the speed of light.

\(\mu_0\) (Permeability of Free Space): \(\mu_0\) is a physical constant that describes how a magnetic field interacts with and modifies a vacuum; its value is approximately \(4\pi \times 10^{-7} \text{ N/A}^2\).