In classical electrodynamics, the average energy density in an electromagnetic field is given by the Poynting vector. In a uniform plane wave, the time-averaged Poynting vector is perpendicular to the direction of propagation and is given by:

⟨ue⟩=1/2⟨E⋅B⟩

where ⟨E⋅B⟩ is the time-averaged value of the dot product of the electric and magnetic fields. The SI unit of energy density is joules per cubic meter (J/m3).

In a plane wave, the electric and magnetic fields are perpendicular to each other and to the direction of propagation. The energy density is therefore:

⟨ue⟩=1/2⟨E⋅B⟩=1/2⟨E⋅H⟩

where H is the magnetic field intensity. The SI unit of energy density is joules per cubic meter (J/m3).

## Other related questions:

### Q: What is the average energy density in the electric field of the wave?

A: The electric field of the wave has an average energy density of E^2/8pi

### Q: What is the formula of energy density of wave?

A: The energy density of a wave is given by:

energy density = wave amplitude squared / (2 * wave speed)

### Q: How do you calculate electric energy density?

A: The electric energy density is given by:

energy density = 1/2 * ε * E^2

where ε is the permittivity of the medium and E is the electric field strength.

### Q: Which is the energy density of a magnetic field?

A: The energy density of a magnetic field is given by:

E = B^2/(2mu_0)

where B is the magnetic field strength and mu_0 is the permeability of free space.