The Human Eye and the Colourful World quiz

The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to:

The human eye forms the image of an object at its:

The least distance of distinct vision for a young adult with normal vision is about:

The change in focal length of the eye lens is caused by the action of the:

Myopia can be corrected by using a:

The colour of light that deviates the least on passing through a prism is:

The phenomenon responsible for the twinkling of stars is:

The blue colour of the clear sky is due to:

The part of the eye that controls the amount of light entering it is the:

A person needs a lens of power -2.5 D for correcting distant vision. The focal length of the lens is:

Why do we have two eyes for vision and not just one? (2 marks)

Why does it take some time to see objects in a dim room when we enter it from bright sunlight outside? (2 marks)

What is hypermetropia? How is it corrected? (2 marks)

Why do stars twinkle? (2 marks)

Explain why the planets do not twinkle. (2 marks)

What is the function of the retina and the optic nerve? (2 marks)

What is a cataract? How can it be treated? (2 marks)

Why does a prism disperse white light while a rectangular glass slab does not? (2 marks)

How does Newton's experiment with two prisms show that white light is made of seven colours? (2 marks)

Why do clouds appear white? (2 marks)

A myopic person has a far point of 80 cm. Find the nature and power of the lens required to correct the defect. (3 marks)

A person cannot see clearly objects closer than 75 cm. Calculate the power of the lens needed to read at 25 cm, and state whether the lens is converging or diverging. (3 marks)

An old person has a near point of 100 cm and a far point of 200 cm. Find the powers of the two parts of the bifocal lens needed, one to read at 25 cm and the other to see distant objects. Name the defect. (3 marks)

The power of the eye lens of a student is found to change so that her near point moves from 25 cm to 40 cm with age. Calculate the power of the convex lens she needs for reading at 25 cm. (3 marks)

The wavelength of red light is about 1.8 times that of blue light. If scattering by very fine particles is much stronger for shorter wavelengths, explain which colour is scattered more and use the data to state why the sky appears blue and the sunset red. (3 marks)

Read the passage and answer the questions. Rohan, a Class 10 student, finds that he can read his textbook easily but has difficulty seeing the writing on the blackboard from the back of the classroom. His eye doctor tells him that his eyeball has become slightly elongated, and that his far point is now 2 m. (i) Name the defect of vision Rohan is suffering from. (ii) Where is the image of a distant object formed in his eye? (iii) Find the power of the lens he needs. (5 marks)

Read the passage and answer the questions. A student passes a narrow beam of white light through a glass prism in a dark room and obtains a band of colours on a white screen. She then places a second identical prism in an inverted position behind the first and finds that white light emerges. (i) Name the phenomenon seen with the first prism and the band of colours. (ii) Why do different colours bend through different angles? (iii) What does the second observation show? (5 marks)

Read the passage and answer the questions. Neha observed that the Sun appeared reddish at sunrise and at sunset but white at noon. She also noticed a beam of sunlight entering a smoke-filled room through a small hole and making its path visible. (i) Why does the Sun appear red at sunrise and sunset? (ii) Why does the Sun appear white at noon? (iii) Name the phenomenon that makes the path of the beam visible. (5 marks)

Read the passage and answer the questions. Mr Sharma, aged 55, finds that he can neither read a newspaper clearly at a normal distance nor see distant road signs well. The optician prescribes bifocal lenses. (i) Name the defect. (ii) What causes this defect? (iii) Describe the structure of a bifocal lens and the purpose of each part. (5 marks)

Read the passage and answer the questions. During a night trip, a group of students observes that the stars twinkle, while Venus and Jupiter appear steady. They also notice that stars near the horizon appear slightly higher than their actual position. (i) Why do stars twinkle? (ii) Why do planets not twinkle? (iii) Why do stars appear higher than they really are? (5 marks)

Describe the structure and working of the human eye with a labelled diagram. Explain the roles of the cornea, iris, pupil, eye lens, ciliary muscles and retina, and explain how the eye adjusts its focal length to see near and distant objects. (6 marks)

What is hypermetropia? State two causes. Draw ray diagrams for (i) a hypermetropic eye (ii) correction of hypermetropia with a convex lens. A hypermetropic person has a near point of 1 m; find the power of the corrective lens to read at 25 cm. (6 marks)

Explain the refraction of light through a triangular glass prism with a labelled diagram, marking the incident ray, refracted ray, emergent ray, angle of incidence, angle of emergence and angle of deviation. Explain why white light splits into its colours. (6 marks)

Explain atmospheric refraction and its effects: (i) twinkling of stars (ii) advance sunrise and delayed sunset (iii) the apparent flickering of objects seen through hot air above a fire. Draw a labelled diagram showing why the Sun is visible before actual sunrise. (6 marks)

What is scattering of light? Explain with a labelled diagram why the sky is blue and why the Sun appears reddish at sunrise and sunset. Describe the Tyndall effect, and explain how the size of the scattering particles affects the colour of scattered light. (6 marks)