Explain the polarization by a thin plastic like sheet.

Explanation

Phenomenon of acquiring plane polarized light from unpolarized light is called polarization.
A sheet by which the polarized light that can be obtained from unpolarized light is called polaroid.
For example : Thin plastic sheet and tourmaline plate.
A polaroid consists of long chain molecules alinged in a particular direction.
Such electric vectors along the direction of the aligned molecules get absorbed and molecules arranged in a perpendicular direction, this direction is called pass axis of polaroid. It passes components of light vectors parallel to the pass axis and perpendicular components are absorbs. So the waves that come out of it will get linearly plane polarized
If the light from an ordinary source passes through a polaroid sheet `P_(1)` its intensity is reduced by half. Rotating `P_(1)` has no effect on the transmitted beam and transmitted intensity remains constant but the intensity on sheet `P_(1)` is less than the intensity of transmitted light.

Now let an identical piece of polaroid `P_(2)` be placed before `P_(1)` and now rotating `P_(1)` the intensity of light coming from `P_(2)` reduces.
When `P_(2)` and `P_(1)` are parallel, the light vectors passes from `P_(2)` also pass through `P_(1)` so the intensity of light is equal to the light transmitted from a `P_(1)` sheet.
When the `P_(2)` sheet is kept in the same position, the `P_(1)` sheet is given `90^(@)` rotation then intensity from `P_(1)` becomes zero. This is shown in figure.

It is shown in figure (a) that light passes through `P_(2)` and `P_(1)` polaroid and by keeping one fixed the relative intensity of the emerging light becomes 1 to 0 as the other polaroid rotates from `0^(@)` to `90^(@)`.

Figure (b) shows that the light (electric) component (polarized light) passing through both polaroids is parallel to the polaroid axis.