Home / Topics / AC Circuits & EM Waves
Energy of EM waves
Intermediate
Energy divided equally between E and B.
Energy density is shared equally by E and B: u = ε₀E² = B²/μ₀. Intensity I = cu_avg.
Sunlight gives 1361 W/m² above the atmosphere.
The energy is in the fields.
In more detail
The energy density of an electromagnetic wave is shared equally between electric and magnetic fields, u = ε0E² in total. Energy flows at the speed of light in the direction of propagation.
Real-world uses
- Solar cells absorb energy from the electromagnetic field of sunlight.
- Radio receivers capture the energy carried by weak waves.
- Solar panels absorb electromagnetic energy, and the energy in a light wave is shared equally between its electric and magnetic fields.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
How is energy split?
Equally between electric and magnetic fields.
Does the wave carry momentum?
Yes, with momentum density equal to energy density divided by c.
Is the energy in a wave equally split?
Yes. In an electromagnetic wave, the electric and magnetic energy densities are equal at every point.
Related topics in AC Circuits & EM Waves
Speed of light · EM wave equation · Relation between E and B · Poynting vector · Intensity of EM wave · Radiation pressure