Electricity & Megnetism

Electromagnetic wave energy

Radio and TV stations emit electromagnetic waves with powers of hundreds of kW

As we have already seen in the study of electromagnetism, a changing magnetic field generates an induced electric field, which is also variable. This variable electric field also generates a variable magnetic field in such a way that the phenomenon is repeated successively. Therefore, we can say that the propagation of these fields does not require the presence of matter to propagate, since electric and magnetic fields can exist in a vacuum.

Thus, we can define electromagnetic wave as the set of variable electric and magnetic fields, perpendicular to each other, that create each other, forming a self-sustaining disturbance that propagates through space.

Electromagnetic waves transport energy from one location to another. This is how the sun’s energy reaches the Earth. The energy of an electromagnetic wave is distributed between the electric and magnetic fields. When propagating, the energy of the wave oscillates between the energy of the electric field and the energy of the magnetic field.

Where ε 0 = 8.85 x 10 -12 C 2 /Nm 2 and E maxis the amplitude of the electric field.

The greater the value of the electric field, that is, the greater the disturbance, the greater the average energy per volume. For example, we know that solar radiation reaching the top of the Earth’s atmosphere has a maximum electric field of 1020 N/C.

Using the previous equation, we can calculate the average energy per unit volume that reaches the atmosphere:

Mean U = 4.6 x 10 -6  J/m 3

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