Draw a diagram to show the refraction of light through a glass prism. On this diagram, mark:

1. Incident ray.
2. Emergent ray, and.
3. Angle of deviation.

When a beam of white light is passed through a prism, it splits to form lights of seven colours. Is it possible to recombine the lights of seven colours to obtain the white light again? Explain your answer.

How could you show that the colours of the spectrum combine to give white light?

Explain why the planets do not twinkle but the stars twinkle.

A person can read a book clearly only if he holds it at an arm's length from him. Name the defect of vision:

1. If the person is an old man.
2. If the person is a young man.

No rainbow could be observed from the surface of Moon by the astronauts. What could be the possible reason?

Explain with the help of a diagram, how we are able to observe the sunrise about two minutes before the sun gets above the horizon.

A person needs a lens of power –5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?

Name the cells on the retina of an eye which are sensitive to

1. Dright light.
2. Dim light.
3. Sensation of colour.

Explain why, we cannot see our seats first when we enter a darkened cinema hall from bright light but gradually they become visible.