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The Human Eye and the Colourful World notes class 10 | Handwritten Notes for science class 10 by ‪@rajansir07‬

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The Human eye
The lens system of the human eye forms an image on the light-sensitive screen called the retina. The cornea is the thin membrane of the eye through which light enters. Most of the light refraction occurs at the outer surface of the cornea. A dark muscular diaphragm that controls the size of the pupil, known as Iris is present behind the cornea. The pupil is a structure in the eye that controls and regulates the amount of light entering the eye. The light-sensitive cells get triggered upon illumination and induce electrical signals. These signals are sent to the brain through the optic nerves. The brain analyses these signals, and finally, processes the information so that we sense objects as they are.

Defects of a Human Eye

Myopia – This is also called as the short-sightedness. A person with this eye defect can only see the nearby objects clearly compared to distant objects. This condition can be corrected using a concave lens.
Hypermetropia – This is also called as farsightedness. A person with this eye defect can only see the distant objects clearly compared to near objects. This condition can be corrected using a convex lens.
Presbyopia – This is an age-related condition caused due to the weakening of ciliary muscles, hardening of the lens, and reduced lens flexibility. A person with this defect usually finds difficulties to focus on nearby objects unable to read or write.

Cataract – This is an age-related condition caused due to the loss of transparency of the lens by erosion of the lens. It usually results in blurry vision, cloudy lenses and can be corrected by replacing the old lens with an artificial lens.

Dispersion of white light by a glass prism

A prism splits the incident white light into a band of seven colours. The band of the coloured components of a light beam is called its spectrum. Isaac Newton was the first to use a glass prism to obtain the sunlight spectrum. Different colours of light bend through different angles with respect to the incident ray, as they pass through a prism. The red light bends the least while the violet the most. Thus the rays of each colour emerge along different paths and thus become distinct.

Atmospheric Refraction

The refraction of light by the Earth’s atmosphere is known as atmospheric refraction. Atmospheric refraction is caused by the bending of light rays when they pass through the layers of the earth’s atmosphere, which are of different optical densities.

Twinkling of Stars

The twinkling effect of stars is due to the atmospheric refraction of starlight. The starlight undergoes continuous refraction as it passes through the atmosphere before it reaches earth. As the path of rays of light coming from the star goes on varying slightly, the apparent position of the star fluctuates and the amount of starlight entering the eye flickers.

Scattering of Light

When a light beam goes through a medium, it hits the particles existing in them. Due to this phenomenon, some of the light rays get absorbed while a few get scattered in various directions. The intensity of the scattered light rays depends on the particles’ size and wavelength.