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Energy density of field
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Energy per volume.
Key relation
u = ½ε₀E²The energy per unit volume of an electric field is u = ½ε₀E². Fields in space carry energy, even in a vacuum.
Worked example
E = 10⁶ V/m: 4.4 J/m³.
Common mistake
Applies to any electric field.
In more detail
The energy density of an electric field is u = ½ε0E², the energy stored per unit volume. It applies to any electric field, not only in capacitors.
Real-world uses
- Estimating energy stored in high-voltage insulation.
- Calculating energy in electromagnetic waves.
- Engineers compare how much energy different insulators can store per unit volume in high-voltage systems.
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Frequently asked questions
What units does energy density have?
Joules per cubic metre.
Is the energy really in the field?
Yes, the field is the storage medium, as shown by electromagnetic theory.
What is the energy density formula?
It is one half times the permittivity times the square of the electric field, for any region of field.
Related topics in Electrostatics
Capacitors in series · Capacitors in parallel · Energy in a capacitor · Dielectrics · Polarisation · Dielectric breakdown