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# unit 2 polarization edexcel ! :s watch

1. hi!

i've been working on the pastpapers and couldn't figure out what the mark scheme means.
so here's the question:

A student looks at the sunshine reflected off a puddle of water. She puts a polarizing (polariod) filer in front of her eyes. As she rotates the filter the puddle appears darker then lighter. Explain this observation.

ans:
1-reflected light is polarized
2-polarised light vibrates/oscillates in one plane/direction,
3-polariod filter only allows vibrations in one direction/plane to pass through
4-when planes are parallel puddle appears light OR when perpendicular the puddle appears dark.

*what is the meaning of point 4 of the ans?

and the other question:
some skier wear sunglasses with polarising lenses, these sunglasses reduce the amount of reflected light entering their eyes. suggest how these sunglasses work.

ans:
1-reflected light is partially polarized
2-polarising filter are at right angles to the plane of polarisation of light.

*what is the meaning of point 2 of the ans?

--is the reflected light (polarized) have horizontal plane of polarization??

thank you sooooo much!!!!
2. (Original post by Lamalam)
hi!

i've been working on the pastpapers and couldn't figure out what the mark scheme means.
so here's the question:

A student looks at the sunshine reflected off a puddle of water. She puts a polarizing (polariod) filer in front of her eyes. As she rotates the filter the puddle appears darker then lighter. Explain this observation.

ans:
1-reflected light is polarized
2-polarised light vibrates/oscillates in one plane/direction,
3-polariod filter only allows vibrations in one direction/plane to pass through
4-when planes are parallel puddle appears light OR when perpendicular the puddle appears dark.

*what is the meaning of point 4 of the ans?

and the other question:
some skier wear sunglasses with polarising lenses, these sunglasses reduce the amount of reflected light entering their eyes. suggest how these sunglasses work.

ans:
1-reflected light is partially polarized
2-polarising filter are at right angles to the plane of polarisation of light.

*what is the meaning of point 2 of the ans?

--is the reflected light (polarized) have horizontal plane of polarization??

thank you sooooo much!!!!
See:

I'll refer to the last link. On the left, the rope oscillates up and down and the polarising filter (the box) has its "hole" vertical. The rope, after passing the filter, still oscillates. Hence there's maximum intensity when the polarising filter is parallel to oscillations. Now look on right of the link. The rope oscillates left and right, but the polarising filter (the box) has its "hole" vertical. The rope, after passing the filter, no longer oscillates. So there's minimum intensity when the polarising filter is perpendicular to oscillations. Can you now understand point 4 in the mark scheme?

------------------------------------
Reflected light is always polarised. A polarised rope would oscillate just up and down or even just left to right etc. An unpolarised rope would oscillate in all planes so left and right, up and down etc so long as they are perpendicular to the direction of the wave travels in. Since the polarising filter is perpendicular to the plane of polarisation of light, the reflected light, which has oscillations in a single plane perpendicular to the direction of wave travel, ends up being blocked and cancelled out (minimum intensity). But this only applies to reflected light. Light directly from the Sun has oscillations in ALL planes perpendicular to direction of wave travel.

Makes sense?
3. yes it makes sense
thank you for your explanation !
4. Reflected light is always polarised. A polarised rope would oscillate just up and down or even just left to right etc. An unpolarised rope would oscillate in all planes so left and right, up and down etc so long as they are perpendicular to the direction of the wave travels in. Since the polarising filter is perpendicular to the plane of polarisation of light, the reflected light, which has oscillations in a single plane perpendicular to the direction of wave travel, ends up being blocked and cancelled out (minimum intensity). But this only applies to reflected light. Light directly from the Sun has oscillations in ALL planes perpendicular to direction of wave travel.

Makes sense? [/QUOTE]

i'm kinda confused :c.
so, polarisation is when the waves go from being lots of them in many directions to just the waves travelling in one direction, right?
i think i get the bits you said about the reflected light... is it that the direction that the wave was travelling in and the direction the filter was, weren't the same so it was blocked? doesn't that just mean it wasn't polarised?
also, with light from the sun.. if you polarise it, does that mean it travels in only one plane?
5. (Original post by pureandmodest)
Reflected light is always polarised. A polarised rope would oscillate just up and down or even just left to right etc. An unpolarised rope would oscillate in all planes so left and right, up and down etc so long as they are perpendicular to the direction of the wave travels in. Since the polarising filter is perpendicular to the plane of polarisation of light, the reflected light, which has oscillations in a single plane perpendicular to the direction of wave travel, ends up being blocked and cancelled out (minimum intensity). But this only applies to reflected light. Light directly from the Sun has oscillations in ALL planes perpendicular to direction of wave travel.

Makes sense?
i'm kinda confused :c.
so, polarisation is when the waves go from being lots of them in many directions to just the waves travelling in one direction, right?
i think i get the bits you said about the reflected light... is it that the direction that the wave was travelling in and the direction the filter was, weren't the same so it was blocked? doesn't that just mean it wasn't polarised?
also, with light from the sun.. if you polarise it, does that mean it travels in only one plane?[/QUOTE]

http://tap.iop.org/vibration/em/312/img_full_46678.gif
http://www.robotroom.com/Polarizers/...zingFilter.gif
http://www.physicsclassroom.com/class/light/u12l1e3.gif
http://cnx.org/content/m42522/latest..._28_08_03a.jpg

Not lots of them. In the first picture initially the wave oscillates in 2 planes of oscillations- horizontal and vertical. The hole polarises the wave by making it oscillate ONLY vertically and so restricting oscillations to a single plane only. This restricting of the plane oscillation is polarisation.

Look at the last picture. Look at the left side. Only if the plane of polarisation is completely perpendicular and so at 90* to oscillations of the wave, the wave gets blocked out and so there's minimum intensity.

http://hyperphysics.phy-astr.gsu.edu...o/sunglass.gif
If you polarise light from the sun, the oscillations are restricted to a SINGLE plane which would be perpendicular to the direction of wave travel (transverse wave).

6. Your final part is correct[/QUOTE]

i'm still kinda confused about the sun bit...
also, could you help me with another question please?
7. ahh wait, i think i get it!! is it because the light from the sun is in the EM spectrum, so it is a transverse wave. Because it's transverse, the disturbance/oscillations are perpendicular to the direction of the wave.
ah, i've just confused myself i thought the waves would start of vertical and horizontal... so which would you take when considering it is perpendicular to the direction of the wave?
sorry btw i'm so bad at physics, but i'm really trying
8. (Original post by pureandmodest)
ahh wait, i think i get it!! is it because the light from the sun is in the EM spectrum, so it is a transverse wave. Because it's transverse, the disturbance/oscillations are perpendicular to the direction of the wave.
ah, i've just confused myself i thought the waves would start of vertical and horizontal... so which would you take when considering it is perpendicular to the direction of the wave?
sorry btw i'm so bad at physics, but i'm really trying
Yes, light from Sun is transverse, so oscillations are perpendicular to direction of wave travel.
http://micro.magnet.fsu.edu/primer/j...avafigure1.jpg
Light from sun would have oscillations in ALL planes, so vertical, diagonal, vertical, ALL...ALL these planes are perpendicular to direction of wave travel. In the pic there are 2 planes of oscillations perpendicular to direction of wave travel.

Don't give up on Physics
9. (Original post by pureandmodest)
ahh wait, i think i get it!! is it because the light from the sun is in the EM spectrum, so it is a transverse wave. Because it's transverse, the disturbance/oscillations are perpendicular to the direction of the wave.
ah, i've just confused myself i thought the waves would start of vertical and horizontal... so which would you take when considering it is perpendicular to the direction of the wave?
sorry btw i'm so bad at physics, but i'm really trying
http://www.olympusmicro.com/primer/i...polfilters.jpg
http://www.microscopyu.com/articles/...ghtfigure1.jpg
http://t3.gstatic.com/images?q=tbn:A...rSMndq6Rr5pqRP
http://t2.gstatic.com/images?q=tbn:A...xZfDS-umw7a-AQ
10. Do we know whether the polarised light from the sun is vertical or horizontal??

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11. (Original post by Lamalam)
Do we know whether the polarised light from the sun is vertical or horizontal??

Posted from TSR Mobile
No

Light directly from sun is unpolarised
See
http://www.physics.uc.edu/~sitko/Lig...s/image002.png

So light from sun has oscillations in many directions perpendicular to direction of wave travel.
12. (Original post by Lamalam)
hi!

i've been working on the pastpapers and couldn't figure out what the mark scheme means.
so here's the question:

A student looks at the sunshine reflected off a puddle of water. She puts a polarizing (polariod) filer in front of her eyes. As she rotates the filter the puddle appears darker then lighter. Explain this observation.

ans:
1-reflected light is polarized
2-polarised light vibrates/oscillates in one plane/direction,
3-polariod filter only allows vibrations in one direction/plane to pass through
4-when planes are parallel puddle appears light OR when perpendicular the puddle appears dark.

*what is the meaning of point 4 of the ans?

and the other question:
some skier wear sunglasses with polarising lenses, these sunglasses reduce the amount of reflected light entering their eyes. suggest how these sunglasses work.

ans:
1-reflected light is partially polarized
2-polarising filter are at right angles to the plane of polarisation of light.

*what is the meaning of point 2 of the ans?

--is the reflected light (polarized) have horizontal plane of polarization??

thank you sooooo much!!!!
This might help a bit (the picture) and also, when light is reflected, depending on the surface it can become plane polarised so most of the light will be in one polarisation rather than a superposition of all states
Attached Images

13. (Original post by krisshP)
No

Light directly from sun is unpolarised
See
http://www.physics.uc.edu/~sitko/Lig...s/image002.png

So light from sun has oscillations in many directions perpendicular to direction of wave travel.
Sorry ! What i mean is actually the light reflected from the water surface, is the reflected light going to be vertically polarised or horizontally polarised?

Posted from TSR Mobile
14. (Original post by Lamalam)
Sorry ! What i mean is actually the light reflected from the water surface, is the reflected light going to be vertically polarised or horizontally polarised?

Posted from TSR Mobile
Not sure. Make a thread on Physics forum on TSR, it's a good question.
15. (Original post by krisshP)
Not sure. Make a thread on Physics forum on TSR, it's a good question.
hello there i happen to have the answer to your question and yeah-> light which reflected from the surface of the water is mainly horizontally polarised. and light from object below the surface of the water is mainly vertically polarised, and so passes through the polarising filter.
16. (Original post by Lamalam)
Sorry ! What i mean is actually the light reflected from the water surface, is the reflected light going to be vertically polarised or horizontally polarised?

Posted from TSR Mobile
hello there i happen to have the answer to your question and yeah-> light which reflected from the surface of the water is mainly horizontally polarised. and light from object below the surface of the water is mainly vertically polarised, and so passes through the polarising filter.
17. (Original post by Brave reader)
hello there i happen to have the answer to your question and yeah-> light which reflected from the surface of the water is mainly horizontally polarised. and light from object below the surface of the water is mainly vertically polarised, and so passes through the polarising filter.
Thanks
18. (Original post by Brave reader)
hello there i happen to have the answer to your question and yeah-> light which reflected from the surface of the water is mainly horizontally polarised. and light from object below the surface of the water is mainly vertically polarised, and so passes through the polarising filter.
Thank you

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