what do you mean by Polaroid filter?

Answer 1

Polaroid filters are capable of selecting a particular polarisation state from an incident light wave. By convention the polarisation of a light wave is specified by the orientation of the electric field.

To the right we imagine an light wave incident from the left onto a polaroid filter. If the incident wave is unpolarised, then one-half of the wave will emerge from the polaroid filter.

We call this orientation of the polaroid zero degrees, and the orientation is indicated by a red arrow.

If the incident wave is unpolarised, then the orientation of the polaroid filter doesn't matter: for any orientation of a perfect filter exactly one-half of the incident wave will emerge. The figures illustrates for an orientation of 45 degrees.
If we place a second filter behind the first with the same orientation, the second filter has no effect: one-half of the incident beam emerges from the first filter and all of that beam emerges from the second filter.

If the first filter is oriented at 0 degrees and the second filter is oriented at 45 degrees, one-half of the light incident on the second polaroid emerges. Thus one-half of one-half = one-quarter of the incident ray emerges from the combination of filters.

Answer 2

Light propagating in a direction has a transverse electric field. A typical polarizing filter removes a portion of the light so that the remaining electric field only oscillates in a single direction (ie. it is polarized light). While the Polaroid company made many types of filters, the term "Polaroid filter" is often taken to mean polarizing filter.

In photography, polarization filters are often used to minimize glare from reflected or scattered light, because both reflection and scattering can partially polarize light.

Answer 3

I guess you mean polarizing filter in photography?

It only accepts light coming from straight ahead. No scattered light. Gives it the ability to lessen some distracting reflections as well as see below the surface of water. Good for shots taken almost into the sun.