Optics - Wave Optics - SS2 Physics Past Questions and Answers - page 5

Polarisation of light refers to the alignment of the electric field vectors of light waves in a specific direction. Unpolarised light consists of randomly oriented electric field vectors. When light passes through a polarising filter or undergoes certain interactions, it can become polarised, meaning its electric field vectors align in a particular direction. Polarised light has properties such as directionality, the ability to transmit through certain filters, and the ability to exhibit interference and diffraction effects. Examples of polarised light include light reflected off a smooth surface, light transmitted through a polarising filter, and light scattered by small particles.

The polarisation of light can occur through various mechanisms. Reflection is one such mechanism, where light waves incident on a smooth surface can become polarised parallel to the surface. This is known as Brewster's law. When light waves pass through a polarising material, such as a polarising filter, transmission can selectively allow light waves with a particular polarisation direction to pass through, while blocking others. Scattering of light by small particles, such as air molecules or dust particles, can also lead to polarisation. When light scatters, the scattered waves can become polarised, with the electric field vectors aligned perpendicular to the direction of scattering. This is known as Rayleigh scattering and is responsible for the polarisation of the blue sky.

Polarised light finds applications in various fields. In photography and cinematography, polarising filters are used to selectively block or enhance certain light waves, reducing glare and improving contrast and colour saturation. In optical microscopy, polarised light can reveal structural details and orientations of materials, aiding in the study of crystals, fibres, and biological specimens. Polarised sunglasses are commonly used to reduce glare and improve visibility, particularly for activities like driving or outdoor sports. Liquid crystal displays (LCDs) rely on polarised light to control the intensity and colour of pixels. Polarised light is also utilised in 3D movie projection, where different polarisations are used for each eye to achieve the perception of depth.