# Properties of Light

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## Reflection of Light

The returning light from the surface of an object when the light is incident on it is called reflection of light. Or in other words, we can say it is the phenomenon of bouncing back light into the same medium by the smooth surface. Examples include a reflection by a plane mirror, glowing stars, moonlight at night etc.

## Laws of Reflection are stated as follows:

(i) Angle of incidence is equal to the angle of reflection.

(ii) The incident ray, the reflected ray and the normal at the point of incidence, all lie in the same plane.

## Refraction of Light

Refraction is the redirection of a wave as it passes from one medium to another. It occurs when a light wave, incident at an angle away from the normal, passes a boundary from one medium into another where there is a change in velocity of the light. It is the most commonly observed phenomenon. Moreover, other waves such as sound waves and water waves also experience refraction.

The refracted wave is determined by the change in wave speed and the initial direction of wave propagation relative to the direction of change in speed.

## Diffraction of light.

It is defined as the bending of light around corners such that it spreads out and illuminates areas where a shadow is expected. Or in other words, we can say it is the slight bending of light as it passes around the edge of an object and the amount of bending depends on the relative size of the wavelength of light to the size of the opening. If the opening is much larger than the wavelength of light, the bending will be almost unnoticeable.

It is hard to separate diffraction from interference since both occur simultaneously. The silver lining which we witness in the sky is caused due to diffraction of light.

## Interference of light.

The phenomenon of multiple light waves interfering with one another under certain circumstances causes the combined amplitudes of the waves to either increase or decrease. This is known as interference of light. Or in other words, we can say it is the phenomenon of addition or superposition of two light waves which produce an increase in intensity at some points and a decrease in intensity at some other points. One of the best examples is the thin film of a soap bubble which reflects a spectrum of beautiful colours when illuminated by natural or artificial light sources.

The interference effect is observed because light reflected from the inner surface of the bubble must travel farther than light reflected from the outer surface, and variations in the soap film thickness produce corresponding differences in the distances light waves must travel to reach our eyes.

## Polarization of light.

Polarisation is a phenomenon induced by the wave nature of electromagnetic radiation. Sunlight is an example of an electromagnetic wave since it travels through the vacuum to reach the Earth. Since an electric field interacts with a magnetic field, these waves are known as electromagnetic waves.

Examples of surfaces that reflect polarized light are undisturbed water, glass, sheet plastics, and highways. In these instances, light waves that have the electric field vectors parallel to the surface are reflected a greater degree than those with different orientations.

## Dispersion of light.

Dispersion is defined as the separation of white light into different colours when the light is passed through the prism. The scattering of light depends on the wavelength of light. Therefore, it can be said that the degrees of deviation is dependent on the wavelengths. The deviation in the path of the light is inversely proportional to the wavelength.

White light is primarily composed of light of different wavelengths (colours) viz. violet, indigo, blue, green, yellow, and red with red having the highest wavelength while violet having the lowest wavelength. The colour red, therefore, deviates the least since it has a maximum wavelength and the colour violet deviates the most since it has the least wavelength. Since all the wavelengths have different angles of deviation, when white light passes from one optical medium to another, different colours of the light split, and this phenomenon of splitting of light into its components as a result of refraction is called dispersion.

## Scattering of light.

Scattering of light is the phenomenon in which light rays get deviated from their straight path on striking an obstacle like dust or gas molecules, water vapours etc. The scattering of light is an important part of our daily life, although we didn’t realize its importance. Scattering of light is different from reflection, as in reflection the radiation is deflected in one direction while in scattering every object or particle can scatter light and illuminates them in all directions.

Scattering of light gives rise to many spectacular phenomena such as the Tyndall effect and the “red hues of sunrise and sunset”. When light passes from one medium to any other medium say air, a glass of water then a part of the light is absorbed by particles of the medium preceded by its subsequent radiation in a particular direction. Some examples of the scattering of light that we come across in day-to-day life are the blue colour of the sky. Out of the seven components present in sunlight, the blue colour is scattered the most by the particles present in the atmosphere and hence, the sky appears blue.