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# How do Polaroid Sunglasses work? OCR Physics E, W and P.

Physics and electronics discussion, revision, exam and homework help.

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1. How do Polaroid Sunglasses work? OCR Physics E, W and P.
Hi, I just want to check I am correct with this, and even if it is correct, is there anything else I could say to improve?

"When sunlight is refected from surfaces, such as the ground, it becomes partially polarised. Polaroid Sunglasses contain polaroid lenses, which can rotate the plane of polarisation by an angle, theta. According to Malus' law, the intensity of light that passes through the polaroid (and hence into the eye) is decreased, as:

Iafter = Iinitialcos2theta."

This is what I would say, but I don't think I am totally correct. These questions are usually worth 2/3 marks, so I think I have waffled to much also.

Thanks for any help
2. Re: How do Polaroid Sunglasses work? OCR Physics E, W and P.
The sunglasses dont rotate the plane of polarisation.

You are right that the light reflecting from a plane surface is partically polarised. The sunglasses contain polaroid lenese which aloow through a particluar plane of polarisation. If they are at 90 to the plane of polarisation of the reflected light then none of that passes through.

(They are usally made so they absorb reflected light from horizontal surfaces like snow or water, thus elimiating reflected glare from the sun)
3. Re: How do Polaroid Sunglasses work? OCR Physics E, W and P.
(Original post by teachercol)
The sunglasses dont rotate the plane of polarisation.

You are right that the light reflecting from a plane surface is partically polarised. The sunglasses contain polaroid lenese which aloow through a particluar plane of polarisation. If they are at 90 to the plane of polarisation of the reflected light then none of that passes through.

(They are usally made so they absorb reflected light from horizontal surfaces like snow or water, thus elimiating reflected glare from the sun)
Thanks for the reply, I think I understand you:

So, the light is reflected from a surface> Becomes Partially polarised > Polaroid lenses in the sunglasses filter out horizontally polarised light but allow through Vertically polarised light > The intensity of light reaching the retina decreases, according to Malus' law I = I0Cos2X.

If not, what would you say to a question that asked "How do Polaroid sunglasses work" for about 3 marks?

Thankyou.
Last edited by ERdoctor; 02-05-2012 at 15:01.
4. Re: How do Polaroid Sunglasses work? OCR Physics E, W and P.
You've got it.

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Last updated: May 3, 2012
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