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# A-Level Physics Polarisation Confusion?? watch

1. I'm really confused about something I was taught today in Physics.

So my understanding of polarisation is that essentially the wave is oscillating in loads of directions and when you used a polariser, it only lets waves oscillating in a specific direction through.

The textbook I had used the analogy of a rope and two gate posts to explain that if the grilles are vertical, it will only let the vertically oscillating part(s) of the wave through (which made sense from a mechanical point of view). The same when the grilles are horizontal; only the horizontally oscillating wave will pass through. I also looked at a few physics videos after the lesson which said the same thing.

Except my physics teacher said that analogy was actually the opposite of the truth. Apparently when the grilles are horizontal, only the vertically oscillating wave passes through (something to do with the direction of the electron oscillation that I really don't understand- someone please explain if so). I also looked at two videos from alevelphysicsonline on youtube- in one he supported the theory presented by the gate and then, in a much later video, he said the same as my physics teacher- that the gate analogy actually tells you the opposite of the truth.

Can someone explain to me which theory it is? It's really confusing me and I'm a little worried that if I write about either of them in my exam, the examiner will mark it as wrong. (my exam board is OCR-A)
2. (Original post by Lydia4512)
I'm really confused about something I was taught today in Physics.

So my understanding of polarisation is that essentially the wave is oscillating in loads of directions and when you used a polariser, it only lets waves oscillating in a specific direction through.

The textbook I had used the analogy of a rope and two gate posts to explain that if the grilles are vertical, it will only let the vertically oscillating part(s) of the wave through (which made sense from a mechanical point of view). The same when the grilles are horizontal; only the horizontally oscillating wave will pass through. I also looked at a few physics videos after the lesson which said the same thing.

Except my physics teacher said that analogy was actually the opposite of the truth. Apparently when the grilles are horizontal, only the vertically oscillating wave passes through (something to do with the direction of the electron oscillation that I really don't understand- someone please explain if so). I also looked at two videos from alevelphysicsonline on youtube- in one he supported the theory presented by the gate and then, in a much later video, he said the same as my physics teacher- that the gate analogy actually tells you the opposite of the truth.

Can someone explain to me which theory it is? It's really confusing me and I'm a little worried that if I write about either of them in my exam, the examiner will mark it as wrong. (my exam board is OCR-A)

For A Level you need to know and understand the analogy with a rope between two fence posts - try not to overthink it.

But your teacher is right (and the video of mine you mentioned is too). With a microwave set up it actually works the other way round due to the way the microwaves are absorbed and then re-emitted by the metal bars). If you're getting confused by this example don't worry about it - any exam questions wouldn't go into this much detail.
3. Let me add something in which students don’t really know or are not told.

When an analogy is used, students should NOT think that the analogy explains the physics. An analogy is like a blackbox which helps to describe the final result but it does not explain the physics. So analogy helps to remember the end result and should not be used as a substitute to explain the physics or further deduce what can happen.

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