Energy in Electric and Magnetic Fields

Both electric fields and magnetic fields store energy. For the electric field the energy density is

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This energy density can be used to calculate the energy stored in a capacitor.

For the magnetic field the energy density is

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which is used to calculate the energy stored in an inductor.

For electromagnetic waves, both the electric and magnetic fields play a role in the transport of energy. This power is expressed in terms of the Poynting vector.