Polarisation and electromagnetic fields

[dt19]

an electromagnetic wave contists of an electric field and a magnetic field oscillating perpendicularly to each other and to the direction of propagation. also, a polariser only let's through light of one particular orientation, so if the polariser is parallel to the direction of the oscillation of the electric field, say, does that mean that on the other side of the polariser there's no magnetic field? I'm having a little trouble getting my head around this!

ta

 

[Tomsk]

No, you can look at a polarizing filter from 2 points of view- either the E field OR the B field. Saying that a polarizing filter filters the E field like this:

|||||||
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is the same as saying the same filter filters the B field like this:
_____
_____
_____
_____

You always have E and B fields making up light, as one field causes the other to be formed.

 

[dt19]

so a polarising filter is really a pair of filters?

 

[Tomsk]

I suppose you could look at them like that, but since they always filter the E field and the B field together, and perpendicularly, you can just consider them to be one filter. You usually only think of what happens to the E field, just by convention. (You could just consider the B field if you wanted, but it just happens to be the E field that is usually considered.) It would be impossible to filter just the E field, say, as if there is no E field, there can't be a B field.