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Physics Polarisation Watch

1. Why is it that when the grille is vertical; that horizontally polarised waves pass through unaffected? Looking at the image, does it not seem logical that only the vertically polarised waves will be allowed through because the grille is vertical? The same applies to the microwave transmitter experiment; when the grille is vertical it blocks the vertically plane polarised waves emitted by the transmitter. But it just doesn't seem right in the diagrams.

2. (Original post by scientific222)
Why is it that when the grille is vertical; that horizontally polarised waves pass through unaffected? Looking at the image, does it not seem logical that only the vertically polarised waves will be allowed through because the grille is vertical? The same applies to the microwave transmitter experiment; when the grille is vertical it blocks the vertically plane polarised waves emitted by the transmitter. But it just doesn't seem right in the diagrams.

I think you are correct and the diagram is wrong. I am having trouble making out the diagram properly though.

Here is an example that is correct:
3. (Original post by scientific222)
Why is it that when the grille is vertical; that horizontally polarised waves pass through unaffected? Looking at the image, does it not seem logical that only the vertically polarised waves will be allowed through because the grille is vertical? The same applies to the microwave transmitter experiment; when the grille is vertical it blocks the vertically plane polarised waves emitted by the transmitter. But it just doesn't seem right in the diagrams.

By convention, the direction of polarisation is the direction of the electric field's oscillations. (Rather than the magnetic)

If the em waves are polarised vertically, the vertical metal conducting grille produces an oscillating electric field that oscillates vertically (a sort of Lenz's Law) and parallel to the field, thus opposing the wave.
If the wave is polarized horizontally, the grille has a minimal effect as the metal bars are now in the wrong direction (now perpendicular to the wave's electric field) to produce this effect.

So it's the vertical electric component that is absorbed by a vertical grille.
4. (Original post by Llewellyn)
I think you are correct and the diagram is wrong. I am having trouble making out the diagram properly though.

Here is an example that is correct:
It's correct. See my other post.
5. (Original post by scientific222)
x
(Original post by Stonebridge)
It's correct. See my other post.
My apologies, your explanation does make perfect sense
6. (Original post by Llewellyn)
My apologies, your explanation does make perfect sense
I think the reason for the confusion is the classic school demo where you pass a rope through a metal grille and, of course, only waves on the rope in the same direction as the grille slits will pass through. This looks good as an explanation, but is a mechanical analogy that doesn't actually relate directly to what's happening in the case of the electric field of the em waves.
7. (Original post by Stonebridge)
I think the reason for the confusion is the classic school demo where you pass a rope through a metal grille and, of course, only waves on the rope in the same direction as the grille slits will pass through. This looks good as an explanation, but is a mechanical analogy that doesn't actually relate directly to what's happening in the case of the electric field of the em waves.
That is the exact analogy I was taught; which made the whole thing confusing.
8. Your picture is totally right. Metal grill is different from polarization filter. The free electrons moving in the metal bar can cancel out the E in that direction and totally absorb it. Thus the horizontal E passes if the grills are vertically positioned. All of the comments above are incorrect.

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Updated: March 25, 2015
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