How is a magnetic field wave produced?

nsaspook

Joined Aug 27, 2009
13,590
So both waves are created at the same time? Or the magnetic field is cause by the electric field?
Crutschow is correct, the electromagnetic field is a dual entity.

There is a widespread interpretation of Maxwell's equations indicating that spatially varying electric and magnetic fields can cause each other to change in time, thus giving rise to a propagating electromagnetic wave[5] (electromagnetism). However, Jefimenko's equations show an alternative point of view.[6] Jefimenko says, "...neither Maxwell's equations nor their solutions indicate an existence of causal links between electric and magnetic fields. Therefore, we must conclude that an electromagnetic field is a dual entity always having an electric and a magnetic component simultaneously created by their common sources: time-variable electric charges and currents."[7]
http://en.wikipedia.org/wiki/Jefimenko's_equations
 

nsaspook

Joined Aug 27, 2009
13,590
So in a radio signal what is the role of the magnetic field? I assume the electric field is the carrier?
They both carry the energy of the wave. Without both there can be no energy flow in the wave, it's like a circuit with a perfect insulator or a superconductor, all voltage with no current or all current with no voltage equals no power. Due to the impedance of free space the ratio of field strength is usually greater in the E field but antennas using primarily the magnetic component of an EM wave are common. Your typical AM ferrite antenna is a good example where we create a low impedance path for a radio signal causing the received magnetic field ratio to be greater.

http://en.wikipedia.org/wiki/Loop_antenna#AM_broadcast_receiver_loop_antennas
 
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