What is a polaroid? State its two uses.

Hint: A polaroid, is similar to a polarizer which produces linear plane polarized light, when unpolarized light passes through it. This usually causes a drop in the intensity of the light as it passes through the polaroid. These polaroids are frequently found to be used in sunglasses and display units such as LCD TV’s, 3-D glasses etc.

Complete step by step solution:
A polaroid is a synthetic dichroic sheet polarizer packed with tiny dichroic crystals, which are oriented parallel to each other, such that any unpolarized light wave passing through it, emerges out as a linearly plane polarized light. However, no other physical quantity such as wavelength, frequency, amplitude or phase of the light changes upon passing through a polaroid.
The natural sunlight emerging from the sun is an example of unpolarized light.
What does an unpolarized light mean then? An unpolarized light is a light wave, having polarization along all the axis, that is the wave contains oscillations along all the axis.
By default, the polarization of an electromagnetic wave refers to the direction of the Electric field of the electromagnetic wave. In an unpolarized wave, the wave contains oscillations along all the axes, hence the electric field seems to be spinning along all the axes for an unpolarized wave.
When, such a wave passes through a polaroid, the oscillation of Electric field along all the axis gets suppressed and only the oscillations that are parallel to the axis of the polaroid are allowed to pass through it, therefore only plane polarized light along the axis of the polaroid emerges out.
In physics, a polaroid is also known as a polarizer.
These polaroids are used in daily life in sunglasses, to reduce the glare and reflections caused, by reducing the intensity of the light passing through the sunglasses as we see through the sunglasses.
Similarly, the polaroids are also used in LCD display’s to manipulate the intensities of the display units as required by the users.

Note: The light emerging from any source is usually unpolarized light, as long as the light does not pass through any polarizing filter. However, we can confirm whether a light is plane polarized or not, by passing the light through a polaroid and rotating the polaroid around the centre.
If the incident light is unpolarized light, the intensity of the emerging light through the rotating polaroid would be of a constant intensity. But, if the incident light is plane polarized light, then the emergent light through the rotating polaroid will not be constant.