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Electric and Magnetic Field Energy Density Calculator.

Calculate vacuum field energy density from electric and magnetic field magnitudes.

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Set your values

Results update as you type.

Electric energy density: 0

Electric energy density

0.000000
Magnetic energy density: 39.788736

Magnetic energy density

0.000000
Total energy density: 39.788736

Total energy density

0.000000

Educational SI model using the assumptions stated above; verify engineering and safety decisions independently.

Use Cases

Physics Homework and Exam Prep

Quickly verify calculations for electromagnetic field energy density problems in vacuum, ensuring correct use of constants and units.

Example: Check the energy density for E = 1000 V/m and B = 0.5 T.

Electromagnetic Wave Analysis

Estimate the energy density of electromagnetic waves in vacuum, useful for understanding wave intensity and energy transport.

Example: Calculate the energy density of a plane wave with given E and B amplitudes.

Frequently Asked Questions

What is field energy density?
Field energy density is the amount of energy stored in an electric or magnetic field per unit volume. In a vacuum, it depends on the square of the field magnitude and the permittivity or permeability of free space.
How is the total energy density calculated?
The total energy density is the sum of the electric and magnetic contributions. The electric part is 0.5 * ε₀ * E², and the magnetic part is 0.5 * (B² / μ₀), where ε₀ and μ₀ are vacuum constants.
What units should I use?
Enter the electric field in volts per meter (V/m) and the magnetic field in teslas (T). The calculator will output the energy density in joules per cubic meter (J/m³).

Tips & Common Mistakes

Tips

  • Ensure your electric field is in V/m and magnetic field in T to get correct results in J/m³.
  • Remember that energy density scales with the square of the field, so doubling the field quadruples the energy density.
  • For waves in vacuum, the electric and magnetic energy densities are equal; you can use this to cross-check your inputs.
  • Use scientific notation for very large or small field values to avoid errors.

Common Mistakes to Avoid

  • Forgetting to square the field values before multiplying by the constants.
  • Using incorrect units, such as kV/m instead of V/m, without converting.
  • Confusing the magnetic field unit T with gauss (1 T = 10,000 gauss).

Last updated: August 13, 2026