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Asked by doppler to Adam, Sheila, Suzie on 24 Mar 2011 in Categories: General.
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Suzie Sheehy answered on 24 Mar 2011:
In an electromagnetic wave (light) the magnetic and electric components are in phase. This is what keeps the light propagating! A magnetic field which varies in time generates an electric field and vice-versa according to Maxwells equations. I think the only reason I can give for ‘why’ is because light wouldn’t propagate if they were out of phase!
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Sheila Kanani answered on 24 Mar 2011:
This is non trivial!! I believe they oscillate in phase but their direction of oscillation is perpendicular, due to Maxwell’s equations.
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Adam Tuff answered on 24 Mar 2011:
As far as I know, magnetic and electric fields are always in phase with each other in light – magnetic components seem to induce electric ones, and vice versa. I’m sure it’s something to do with propagation, but I’m not too sure!
Comments
doppler commented on :
This has been confusing me a bit because in textbooks they’re almost always drawn in phase (i.e. with both electric and magnetic components at minimum amplitude at the same time), but in that case wouldn’t the energy in the overall system be changing? E.g. if both fields had a minimum amplitude at the same time, wouldn’t the system have no energy at that instant…? whereas if they were out of phase by pi (I think?) the overall energy would be conserved…