Energy in Electromagnetic Waves

• Electromagnetic waves contain energy. We know already expressions for the energy density stored in E and B fields:

• The Intensity of a wave is defined as the average power transmitted per unit area = average energy density times wave velocity:

• For ease in calculation, define Z0 as:

• In an e-m wave, B = E/c

• Therefore, the total energy density in an e-m wave = u, where

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