Light will not pass through a pair of polaroid filters when they are aligned perpendicularly. But, if a 3rd...

Question

polaroid filter is sandwiched between the other 2 with its alignment halfway between the alignment of the others(that is with it's axis making a 45 degree angle with each of the other two)some light goes through. WHY?


I know that a small amt of shorter wavelenghts can get through but there must be more to it. Can you help me out?

Answer 1

In order to answer this question, you'll first have to know something about light. Light can be regarded as a flow of particles (called photons), or as an electromagnetic wave. I'll try to stick to the wave theory. So, light can be regarded as a waveform, oscillating in an arbitrary direction perpendicular to its direction of motion. There will be waves oscillating up/down, oscillating left/right and all that's in between those two.

A polaroid filter only allows to pass that component of the oscillation, directed in the polarizing direction of the filter. So only the waves that are oscillating in the polarizing direction can pass the filter unattenuated. All other waves will attenuate according to the formula:



Amplitude after polarizing = Amplitude before polarizing * cos (theta),
where theta is the angle between the oscillating direction of the wave and the polarizing direction of the filter.

The overall effect is blocking out half of the available light, and 'directing' the other half.

In your case, where you have a total of 3 filters, the inner filter "channels" a small amount of light along the interim filter so that it hits the perpendicular filter at an angle that it would not otherwise be traveling along.

Answer 2

Solly got it right. A polarizing filter 'projects' the electric field of the light onto the direction of the filter. If you send light through the first filter, all the light coming out is vibrating in the diection of the polarization. Now, a second filter perpendicular just 'quashes' everything to zero. But one aligned at 45 degrees gives a non-zero projection. The third filter then projects the new orientation to the last filter. That projection is no longer zero.

Answer 3

Polarizing filters aren't perfect. Their purpose is to pass light of only one polarization. Not only do they do that imperfectly, but they also change the polarization of the light to some degree, especially if they contain a birefringent layer. The effect here is the third filter changing the polarization of the light which passed the first filter, so that it can now pass the second.

Replace that third filter by some crystalline substances like calcite or mica and you can see some really cool effects, as the crystal changes the polarization also.

Answer 4

hi, between your different physics questions you have asked until now you will think of you have been attempting to strengthen a semiconductor production technique on your basement! sturdy success with that. in case you decide on any HEPA filtration suggestion i ought to help you out.