Energy Density Calculator

What Is Electromagnetic Energy Density?

Electric and magnetic fields store energy in space. Energy density tells you how many joules are stored in each cubic meter of vacuum at a given field strength.

Energy Density Formulas

Electric field contribution:

$$u_E = \frac{1}{2}\epsilon_0 E^2$$

Magnetic field contribution:

$$u_B = \frac{B^2}{2\mu_0}$$

Total energy density in vacuum:

$$u = u_E + u_B$$

with $\epsilon_0 \approx 8.854 \times 10^{-12}\,\text{F/m}$ and $\mu_0 \approx 4\pi \times 10^{-7}\,\text{H/m}$.

Example: $E = 1000\,\text{N/C}$ and $B = 0.01\,\text{T}$ gives total density near 39.8 J/m³, mostly from the magnetic term.

Frequently Asked Questions

What are the units of energy density?

Joules per cubic meter (J/m³) in SI units. It is energy stored per unit volume.

Which term dominates for strong magnetic fields?

The magnetic term grows with $B^2$. Even modest fields can store far more energy than weak electric fields.

Do these formulas apply in materials?

This calculator uses vacuum constants. Inside materials, use the local permittivity and permeability values.

Where is field energy density important?

Capacitors, inductors, electromagnetic waves, and plasma physics all rely on stored field energy.

Can either field term be zero?

Yes. A pure electric field gives only $u_E$. A pure magnetic field gives only $u_B$. Most waves contain both.

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What Is Electromagnetic Energy Density?

Energy Density Formulas

Frequently Asked Questions

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