Energy density

Definition

Energy density is the amount of energy stored in a given system or region of space per unit volume. It is often used to describe the energy stored in capacitors and electromagnetic fields.

5 Must Know Facts For Your Next Test

1. Energy density in a capacitor is given by $u = \frac{1}{2} \varepsilon E^2$, where $u$ is the energy density, $\varepsilon$ is the permittivity, and $E$ is the electric field.
2. In an electromagnetic wave, the energy density can be split into electric and magnetic components: $u = u_E + u_B$, where $u_E = \frac{1}{2} \varepsilon E^2$ and $u_B = \frac{1}{2} \mu H^2$.
3. The total energy stored in a capacitor can be found by integrating the energy density over its volume.
4. For electromagnetic waves in a vacuum, the energy density ratio between electric and magnetic fields remains constant: $\frac{E}{B} = c$, where $c$ is the speed of light.
5. Energy density plays a crucial role in determining how much energy can be stored or transmitted by capacitors and electromagnetic waves.

Review Questions

• What formula represents the energy density stored in a capacitor?
• How do you calculate the total energy stored in a capacitor from its energy density?
• What is the relationship between electric and magnetic field components of energy density in an electromagnetic wave?

Related terms

Capacitance:

The ability of a system to store charge per unit voltage; measured in farads (F).

Permittivity:

A measure of how much resistance is encountered when forming an electric field within a medium.

Electromagnetic Wave: A wave consisting of oscillating electric and magnetic fields, which propagates through space carrying energy.