The human eyeis an organ that detects light and allows us to see. It works like a camera by focusing light onto the retina, which sends signals to the brain to form an image.
Parts of the Human Eye:
- Cornea – Transparent outer layer that refracts light.
- Pupil – The dark circular opening that controls the amount of light entering the eye.
- Iris – The colored part of the eye that controls the size of the pupil.
- Lens – Focuses light onto the retina.
- Retina – The light-sensitive layer at the back of the eye where images are formed.
- Optic Nerve – Transmits the visual information from the retina to the brain.
Working of the Eye:
- Light enters through the cornea and pupil.
- It is focused by the lens onto the retina.
- The retina converts the light into nerve signals, which are sent to the brain through the optic nerve.
The Colourful World:
The world appears colourful because light from the sun is made of different colours (the spectrum of light).
- Dispersion of Light:When white light passes through a prism, it splits into its seven colours (violet, indigo, blue, green, yellow, orange, and red) — this is called dispersion.
- The Formation of Rainbow: A rainbow is formed when sunlight is refracted and dispersed by water droplets in the sky, creating a spectrum of colours.
- Why the Sky Appears Blue: The blue light from the sun is scattered more than other colours due to its shorter wavelength, making the sky look blue.
Practice Questions PDF
Download a printable worksheet on The Human Eye and the Colourful World with answers.
Questions on The Human Eye and the Colourful World
Showing 1–30 of 821.Define the terms 'near point' and 'far point' for the human eye. What are their normal values for a healthy young adult? 2.Assertion (A): The Sun appears elliptical at sunrise and sunset. Reason (R): Atmospheric refraction causes the Sun's apparent vertical diameter to decrease more than its horizontal diameter, leading to an elliptical appearance. 3.Why do raindrops cause dispersion of white light to form a rainbow, but air bubbles in water do not produce a similar visible spectrum? 4.Is the image formed on the retina real or virtual? Is it inverted or erect? 5.Emergency exit signs in buildings are often green. What scientific reason supports this choice, considering human vision? 6.In the dispersion of white light by a prism, which colour deviates the most and which deviates the least? What is the reason for this difference in deviation? 7.A person needs a concave lens of power -4.5 D for correcting his distant vision. Calculate the focal length of the corrective lens and the distance of his far point. 8.If the Earth had no atmosphere, what would be the colour of the sky during the day? 9.If a beam of white light is passed through a glass slab, parallel to its base, it emerges as white light. However, if it passes through a glass prism, it disperses into its constituent colours. Explain this difference. 10.What is cataract, and how is it corrected? 11.Why is there a difference in the extent of scattering of red and blue light by the atmosphere? 12.A person has a near point of 100 cm and a far point of 500 cm. He wants to be able to read a book at 25 cm and see distant objects. Calculate the powers of the bifocal lenses he needs. 13.Why does the pupil of the eye appear black? 14.Two prisms, one made of crown glass and the other of flint glass, are used. For a given angle of incidence, which prism would produce a greater dispersion of white light and why? 15.Which type of photoreceptor cells are primarily responsible for our ability to differentiate colours? Where are they most concentrated? 16.Why is red light scattered the least compared to other colours in the visible spectrum? 17.What is meant by the 'power of accommodation' of the human eye? 18.A student is unable to see the words written on the blackboard clearly when sitting on the front bench, but he can read the book in his hand without any problem. Identify the eye defect and suggest the type of lens to correct it. 19.Explain the phenomenon of 'persistence of vision' and its application. 20.A person needs a concave lens of focal length 50 cm to correct his distant vision. What is the farthest distance this person can see clearly without corrective lenses? 21.Why do clouds generally appear white? 22.Why are danger signals usually red in colour? 23.Why do different colours of light bend at different angles when passing through a prism? 24.Can a person with colour blindness see any colours at all? Explain briefly. 25.The near point of a hypermetropic person is 75 cm from the eye. Calculate the power of the lens required to enable him to read clearly a book held at 25 cm from the eye. 26.A child has difficulty seeing objects far away but can read a book comfortably. What is his eye defect? What kind of lens would a doctor recommend? 27.Which part of the eye is donated in eye donation, and why is it important? 28.Why does a glass prism cause dispersion of white light, while a hollow prism or a glass slab does not? 29.How does the human eye change its focal length to focus on objects at different distances? 30.Assertion (A): Red colour is used as a danger signal. Reason (R): Red light has the longest wavelength and is scattered the least by smoke or fog.