Unpolarised light can be transformed into polarised light. Light waves that are polarised have oscillations of electric fields that occur in a single plane. Polarisation is the process of converting unpolarised light into polarised light. Polarising light can be done in a variety of ways.

The four methods are – 

Polarisation by Transmission

Polarisation by Reflection

Polarisation by Refraction

Polarisation by Scattering 

A light wave could be an electromagnetic wave that travels through the vacuum of outer space. Light waves are made by moving electric charges. An electromagnetic wave is a transversal wave that has an electrical and a magnetic component.

A light wave that oscillates electric fields in addition to one plane is observed as unpolarized light. lightweight emitted by the sun, by a lamp within the classroom, or by light is unpolarized light. Such light waves are created by a number of electric charges that vibrate, therefore making an electromagnetic wave that oscillates the electric field in a variety of directions. This idea of unpolarized lightweight is quite troublesome to visualise.

What is Polarisation?

Light waves are transverse: that is, the vibrating electric vector associated with each wave is perpendicular to the direction of propagation. A single vertical oscillation of light waves can pass through a vertical slit. Still, when a horizontal light wave oscillating passes through a vertical slit, it cancels and gets blocked by the slit. Thus, a plane-polarised light is a light wave that oscillates along a single plane. This process of converting unpolarised light into a plane-polarised one is known as polarisation. Polarisation is used in polaroid cameras, sunglasses, lenses, laboratories, polaroid sheets, etc.

Polariser

A device for converting unpolarised light into a plane-polarised one is a polariser. A polariser is usually a polaroid sheet. A polaroid film or a polaroid sheet consists of molecules arranged in parallel columns to each other. The space between any two adjacent columns in the molecules of the sheet acts to allow light with only a specific orientation to pass through. They are spaced and arranged in such a way to allow only one desired plane of light to pass through. All other lights with an electric field that do not have the same orientation are absorbed. In this way, all the unpolarised light transforms into plane-polarised or polarised light. 

The transmission axis of any polaroid sheet is always perpendicular to the orientation of the column of the molecule.

Uses of a Polariser

• Liquid crystal display — Typically used in calculators, mobiles, digital watches, and such products. Whenever we press a button, that area becomes slightly warm. In some cases, current passes through them, undergoes chemical changes and becomes liquid. This liquid chemical acts as a polariser and does not allow light to pass from that area. Thus, we can see numbers written in black in calculators; the liquid polarisers make numbers appear black due to a lack of light.
• Aeroplane windows — While flying at heights, the windows of aircraft are made in such a way to avoid the UV rays and other unnecessary lights.
• 3D effect on a picture — Each eye sees an image from two different angles. Our brain sees it as a 3D object, as it can perceive depths from these images. While creating such movies, one image is taken from horizontally polarised light and the other from a vertically polarised light. Polarised glasses have two different lenses for each eye, polarised per the images. The resultant image that we see is a 3D image perceived by the brain, whereas without the glasses, one sees the same image in 2D.
• Polaroid camera — Here, a light-sensitive film is exposed to light coming from the source to capture the image. A light-sensitive chemical, silver halide, is used. The light falling on this film disturbs the molecules of silver halide. This incident light produces energy that ionises the molecules. This ionisation causes individual silver atoms to release, and the amount of silver atoms produced is directly proportional to the amount of exposed light. Thus, the area with more light is darker due to excess silver. This negative picture is converted into a positive with further chemical reactions to get a coloured image.
• Chemical analysis — When a polarised light passes through a chemical, its crystals may turn the direction of the light to the left or the right. This helps in the identification of the chemical or in checking the concentration of the chemical. 
• Glare reduction — At night, while driving, one cannot see the vehicle’s headlight approaching head-on because our eyes’ lenses adjust to absorb maximum light. While doing so, if the headlights of another vehicle focus on our eyes, they tend to get more light than needed; thus, the lenses in our eyes adjust themselves to a smaller size to perceive the headlight. While doing so, other nearby objects in the dark are not visible to us. This may cause accidents. Cars’ headlights have vertical polaroids on them to avoid this. These polaroids reduce the intensity of the lights.

Conclusion

Vehicles, smartwatches, calculators, laptops, mobiles, television screens, railways station indicators, vehicles, aircraft, and such implement polaroids. One can even see the use of polarisers more clearly in the lens of cameras. The lens of a camera is a polaroid. While placing two lenses in front of each other and rotating them against a light source, we can see an alternate dimming of the light. This is due to the direction in which they are polarised. With such vital applications, a polariser is used almost in everything in our day-to-day lives.