Polarising Light

Webmonkey

This just popped into my head now.
Ok some of you know that to prove light is a transverse wave is by polarising it. Shine it through one sheet of polaroid to split it to one plaine and then another polariod at 90degrees to stop the light polarising on the final plane.
But the weird thing is, if you put a third sheet of polaroid the light re appears,

whats the story with that?

dudara

One turn closes off one plane, another closes off the second and the third brings you back to one plane. Polarising the light by passing it through 2 sheets of Polaroid is not killing the light, per se, it's just polarising it.

Webmonkey

I understood polarising as stopping the light. That explains a lot then

ApeXaviour

dudara wrote:

One turn closes off one plane, another closes off the second and the third brings you back to one plane. Polarising the light by passing it through 2 sheets of Polaroid is not killing the light, per se, it's just polarising it.

Hmm.. Seems skipping all optics related exam questions / lectures over the last three years has left me with some gaps.
Okay so if you pass light of a visible wavelength through two sheets of polaroid at 90° to eachother no light is visible on the other side. But you're saying it's still there, maybe you could enlighten me as to what form it takes?

_Dubh_

I believe the actual polaroid paradox is as follows:

Polaroid A is horizontal so that photons with electric oscillation of 0 degrees
only gets through. Then Polaroid B is placed behind it at 90 degrees to the horizontal (vertical) no light gets through.

However, if you place Polaroid C at 45 degrees to the horizontal inbetween the two some light will get through.


I haven't actually heard of the 0 - 90 - 0 arrangement before.

ApeXaviour

Cheers dubh. That's cleared it up entirely for me.. thanks

dudara

Here's a better description

nesf

Cheers dudara

I'm sure I got a lecture on this in optics but I can't for the life of me remember it!

causal

dudara wrote:

Here's a better description

That's a fun physics lecture, in addition to the diagrams, the quotes I'd note would be:

for light travelling in a particular direction, the plane in which the electric (and magnetic) field is oscillating is not fixed and indeed the electric field can oscillate in any plane which is perpendicular to the direction of propagation.
<snip>
...appreciated the vector nature of the electric field in so far as the magnitude and direction can change as the light passes through each polaroid.

I never was big on writing down everything the lecturer said

causal