CBSE The Human Eye and the Colourful World Subject Notes
CBSE Guess > eBooks > Class X > The Human Eye and the Colourful World by Mr Sunil D Chauhan
The Human Eye and the Colourful World
The Human Eye and the Colourful World
Advance sunrise and delayed sunset We can see the sun about 2 minutes before the actual sunrise and 2 minutes after the actual sunset because of atmospheric refraction. So the length of the day is increased by 4 minutes.
Scattering of sunlight Light is scattered when it falls on various objects. The colour of the scattered light depends on the size of the scattering particle. Very fine particles scatter mainly blue light while particles of larger size scatter light of longer wavelengths i.e. red colour. If the size of the particle is very large, the scattered light may appear white.
Tyndall effect The scattering of light by colloidal particles in their path is called Tyndall effect. Tyndall discovered that when white light is passed through a clear liquid having small suspended particles in it, the blue colour of white light having shorter wavelength is scattered much more than the red colour having larger wavelength.
Colour of the sky is blue Colour of the sky is blue because when sunlight passes through the atmosphere, the fine particle in the air scatter the blue light of shorter wavelength more strongly than red and the blue light enters our eye.
White colour of clouds Clouds are seen due to scattering of light from lower parts of earth's atmosphere containing large particles of dust, water, etc. So all the colours are scattered equally and the clouds appear white.
What would happen in absence of atmosphere?
If the earth has no atmosphere, the atmospheric refraction would not take place and we would see the actual sunrise and sunset. The day would have been shorter by 4 minutes. Also, there would not have been any scattering and the sky would have looked dark.
Danger signals are red in colour Danger signals are red in colour because the red colour is scattered least by smoke and fog and so can be seen from a longer distance due to its longer wavelength.
Sun appears red at sunrise and at sunset Light from the sun near the horizon has to travel the larger distance through thicker layers of atmosphere. Due to this, most of the blue colour present in the sunlight has been scattered out and most of the red colour reaches our eye.
Stars appear to be twinkle while planets do not. The continuously changing atmosphere causes variations in the light coming from point sized star due to refraction. So the stars appear to be twinkle. The atmospheric refraction cannot cause variations in the light coming from big sized planets and they do not twinkle.
Glass prism forms spectrum while glass slab does not A glass slab can be assumed as the combination of two prisms. The first prism decomposes the white light into seven colours and the second prism (placed inverted) recomposes the seven colours into white light. It takes some time to see the image clearly when enter into dim room.
When we enter into a dim room, the iris takes some time to adjust the size of the pupil so that more amount of light may pass through it.
- The blue coloured light present in white light is scattered 10 times more easily than the red light.
- Very fine particles mainly scatter blue light
- For a myopic person, u = 8 and for a hypermetropic person u = - 25cm.
- At very high altitudes, there is nothing to scatter the sunlight. So the sky appears dark to the astronauts.
