polaroid effect

[keltiejack]

It is well known that if you take two pieces of polaroid sheeting, and place them on top of each at "right angles" the vast majority of light is cut out. What is less well known, is that if you take a third piece, and place it between the first two sheets then the "light" reappears.It does not make sense.Try it ! Is there a SIMPLE explanation?

[keltiejack]

for anyone trying to make sense of this question

the phrase " is a quotation mark !

[keltiejack]

still not making sense!

In the question I typed ", it came out ".In my not above I typed what had come on screenand got "

[jake-the-peg]

It's because a polaroid filter isn't doing what you think it's doing.

Look at a piece of polaroid - if it were stopping all light apart from the small fraction that is in exactly the right alignment you'd get very little light through - how much light do you think is actually getting through 25% 30%? Does this fit in with the traditional explanation of how a polarising filter works?

It's explained nicely here
http://alienryderflex.com/polarizer/

[keltiejack]

thanks jake-the -peg
I have had a look at your reference, and I have to admit I am not a lot wiser.I must be thick.I'm not that thick,I used to teach chemistry beyond A level.
Thanks anyway!

[jake-the-peg]

The point is that the polarising filter does not simply block out light that is incorrectly polarised which is how it is often explained.

It does block light that is at 90 degrees but light that is at say 45 degrees to the axis of polarisation will partly reinforce the transmitted light.

Imagine you have 3 rays of intensity I one at 90 degrees one at 0 degrees and 1 at 45 degrees.

What you do not get is 1 polarised beam of Intensity I transmitted.

The 0 degrees beam is transmitted entirely (I)
The 90 degree beam is blocked entirely (0)
A component of the 45� beam is transmitted (Isin(45�))

Rather than thinking of it as only letting through light at 0�think of it as the polarising light is only blocking light at 90� and the light at other angles is being twisted

[keltiejack]

Thanks again, I think that helps