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polarization........

I'll file the attachment to the question below.. and my attempt to it..
I get why its not A or C, because for A oscillations can be in either X and Y direction.. And for C, that would be describing a longitudinal wave... so answer is either B or D.. but its D.. somehow. I figured it'd be B because if it were in a plane perpendicular to X direction... then oscillations would be perpendicular to Z, which is direction of wave propagation.... help.
Reply 2
Original post by Abraham_Otaku
I get why its not A or C, because for A oscillations can be in either X and Y direction.. And for C, that would be describing a longitudinal wave... so answer is either B or D.. but its D.. somehow. I figured it'd be B because if it were in a plane perpendicular to X direction... then oscillations would be perpendicular to Z, which is direction of wave propagation.... help.


"Perpendicular to the x direction" means that it could be parallel to z, since z is perpendicular to x. It's not though, because z is the direction of propagation.
(edited 1 year ago)
Original post by Sinnoh
"Perpendicular to the x direction" means that it could be parallel to z, since z is perpendicular to x. It's not though, because z is the direction of propagation.

Thanks for reply but.... I still don't understand... Shouldn't the oscillations be in a plane which includes the direction of wave propagation.. so in this case the plane should include the wave propagation in Z direction?
Reply 4
Original post by Abraham_Otaku
I get why its not A or C, because for A oscillations can be in either X and Y direction.. And for C, that would be describing a longitudinal wave... so answer is either B or D.. but its D.. somehow. I figured it'd be B because if it were in a plane perpendicular to X direction... then oscillations would be perpendicular to Z, which is direction of wave propagation.... help.

Transverse waves vibrate at right angles to the direction of energy transfer.
So it makes sense to be D
Original post by 2022 g
Transverse waves vibrate at right angles to the direction of energy transfer.
So it makes sense to be D

I mean yes but... they're talking about planes of oscillations... which is whats confusing me..
Reply 6
Original post by Abraham_Otaku
I mean yes but... they're talking about planes of oscillations... which is whats confusing me..

Ok basically the direction of energy transfer is ‘z’
Since the it vibrates at right angles as i said before. Which means that oscillations will take place at right angles to the direction of energy transfer (z).
Hence the direction of oscillation will be perpendicular to the direction of z
The term vibration is used to describe the oscillation, I’m pretty sure.
(edited 1 year ago)
Original post by 2022 g
Ok basically the direction of energy transfer is ‘z’
Since the it vibrates at right angles as i said before. Which means that oscillations will take place at right angles to the direction of energy transfer (z).
Hence the direction of oscillation will be perpendicular to the direction of z
The term vibration is used to describe the oscillation, I’m pretty sure.

sorry if I'm being annoying but could you explain it in terms of the planes.. I understand that the oscillations have to be perpendicular to the Z direction.. but not the planes stuff...
Reply 8
Original post by Abraham_Otaku
Thanks for reply but.... I still don't understand... Shouldn't the oscillations be in a plane which includes the direction of wave propagation.. so in this case the plane should include the wave propagation in Z direction?


The oscillations should not be in a plane which includes the direction of wave propagation, because it's a transverse wave. There are two oscillations happening - magnetic and electric fields. A plane containing both of those oscillations has 0 z component.
Imagine the oscillations as a vector. The vector will have its base at some point on the z axis, but its direction will be along either the x or y axes, and will have no z component. It can't be oscillating forwards and backwards along z, because it's travelling in that direction and it's not longitudinal.
(edited 1 year ago)
Original post by Sinnoh
The oscillations should not be in a plane which includes the direction of wave propagation, because it's a transverse wave. There are two oscillations happening - magnetic and electric fields. A plane containing both of those oscillations has 0 z component.
Imagine the oscillations as a vector. The vector will have its base at some point on the z axis, but its direction will be along either the x or y axes, and will have no z component. It can't be oscillating forwards and backwards along z, because it's travelling in that direction and it's not longitudinal.

but isn't the definition of polarized light one where the oscillations are in a single plane which includes direction of wave propagation??.. that's what they taught in As level.. and show it in markschemes as well..
Original post by Abraham_Otaku
but isn't the definition of polarized light one where the oscillations are in a single plane which includes direction of wave propagation??.. that's what they taught in As level.. and show it in markschemes as well..


Yes literally. With polarised light it goes in one plane but it oscillates perpendicular to the direction of the plane.
8A31161B-6723-4EDE-AA67-575D8ADB0EF9.jpeg

Polarising filter*
All you need to do is understand the concept.
Polarising waves are only transverse waves.
(edited 1 year ago)
Original post by 2022 g
8A31161B-6723-4EDE-AA67-575D8ADB0EF9.jpeg

Polarising filter*
All you need to do is understand the concept.
Polarising waves are only transverse waves.

I see.... I think I understand it now.. though still slightly confused, but I understand. Thanks:smile:
Original post by Abraham_Otaku
I see.... I think I understand it now.. though still slightly confused, but I understand. Thanks:smile:

Do some more practice questions and it will hopefully give you a better understanding. The more practice the better!
Goodluck!!:rolleyes:
Original post by Abraham_Otaku
but isn't the definition of polarized light one where the oscillations are in a single plane which includes direction of wave propagation??.. that's what they taught in As level.. and show it in markschemes as well..

Ok, this is what is going on:
poynting.jpg
The oscillations & their directions are represented by the arrows; for one of the fields, the plane contains the z-axis, along which the wave is propagating. But the oscillations themselves are not along the z-axis, they're perpendicular to it.
Hence why B is wrong - oscillations along the x-axis are fine, because the x-axis is perpendicular to the direction of propagation.
Maybe putting the question pic with an animated em wave can speak of a "clearer explanation".
(edited 1 year ago)

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