Wonders of Light – Part II – Maharashtra Board Class 10 Solutions for Science and Technology (English Medium)
1. The phenomenon of splitting of light into its component colours is dispersion.
2. Very fine particles mainly scatter blue light
3. The phenomenon of change in the direction of propagation of light when it passes from one transparent medium to another is refraction.
4. The refractive index depends upon the velocity of propagation of light in different media.
The phenomenon of splitting of light into its component colours is called dispersion of light.
The different colours of light in the spectrum of light are violet, indigo, blue, green, yellow, orange and red.
The formation of a rainbow in the sky is a combined result of dispersion, refraction and reflection of sunlight by water droplets present in the atmosphere after a rain shower.
When sunlight is incident on a water droplet, there is
1. Refraction and dispersion of light as it passes from air to water.
2. Internal reflection of light inside the droplet.
3. Refraction of light as it passes from water to air. The water droplets act as small prisms. The refractive index of water is different for different colours. It is maximum for violet and minimum for red. Hence, there is dispersion of light into seven colours. Thus, a rainbow is formed with red colour at the outer side and violet colour at the inner side and the remaining five colours lie in between.
The phenomenon of a change in the direction of propagation of light when it passes obliquely from one transparent medium to another is called refraction of light.
For a given angle of incidence, the extent of refraction of light is different in different media.
1. When the refractive index of the second medium is greater than the refractive index of the first medium, more is the bending of the refracted ray towards the normal.
2. When the refractive index of the first medium is greater than the refractive index of the second medium, lesser is the bending of the ray of light away from the normal.
1. For an observer on the Earth, the sky appears blue because of scattering of sunlight by the molecules of air and other particles of the atmosphere around the Earth.
2. The same sky appears dark to a person in space because there is no atmosphere at a high altitude, so the scattering of light does not take place.
Stars are far away from the Earth, and they emit their own light. So, they can be taken as a point source of light. Starlight gets refracted from the atmospheric medium with a varying refractive index. As starlight bends towards the normal, the apparent position of the star is slightly higher than its actual position.
The Sun is very close to the horizon early in the morning, as sunlight travels a longer path through the atmosphere before reaching the observer. The blue and violet light are scattered much more than the red light by the Earth’s atmosphere. So, they are scattered away from the path of light because of the greater thickness of the atmosphere. Hence, the light reaching the observer on the Earth’s surface is mostly red and yellow. Therefore, the Sun appears reddish early in the morning.
A rainbow can be seen as a combined result of refraction, dispersion and reflection of sunlight by water droplets present in the atmosphere after it has rained. When there is no rain, a fountain can serve as a source of fine droplets. These water droplets in sunlight can produce a rainbow. So, it is possible to enjoy a rainbow at fountains in any season.
1. When a ray of light passes obliquely from one transparent medium to another, it changes its path and is called refraction.
2. The extent of refraction depends on the density of the medium.
3. Atmosphere is never static. Air is mobile; its density and temperature vary. Hence, the refractive index of the atmosphere also varies. The refractive index of cool air is greater than that of hot air.
4. Due to atmospheric reflection of light, we observe many optical phenomena such as twinkling of a star, advanced sunrise and delayed sunset, mirage and flickering of an object seen through a turbulent stream of hot air rising from a fire.
The phenomenon of splitting of light into its component colours is called dispersion of light. When white light passes through a glass prism, it spreads out into a band of different colours called the spectrum of light. The colours in the spectrum of white light are violet, indigo, blue, green, yellow, orange and red. Formation of a rainbow is an example of dispersion of light in nature. In this case, raindrops act as a glass prism and you get dispersion of sunlight.
Dispersion takes place because the refractive index of a material such as glass or water is different for different colours. It is maximum for violet colour and minimum for red colour. Hence, through a prism, violet light is deviated the most and red light is deviated the least. The other colours lie in between.