Name the atmospheric phenomenon due to which the sun can be seen above the horizon about two minutes before actual sunrise.

If a milky of cloudy membrane grow over the eye lens, then which defect is the person suffering from?

Why do stars twinkle?

A man can read the number of a distant bus clearly but he finds difficulty in reading a book.A man can read the number of a distant bus clearly but he finds difficulty in reading a book.

1. From which defect of the eye is he suffering?
2. What type of spectacle lens should he use to correct the defect?

When we place a glass prism in the path of a narrow beam of white light a spectrum is obtained. What happens when a second identical prism is placed in an inverted position with respect to the first prism? Draw a labelled ray diagram to illustrate it.

Ciliary muscles of human eye can contract or relax. How does it help in the normal functioning
of the eye?

Nocturnal animals (animals which sleep during the day and come out at night) tend to have wide pupils and lot of rods in their retinas. Suggest reasons for this.

A student sitting in the last row of the class-room is not able to read clearly the writing on the
blackboard.

1. Name the type of defect he is suffering from.
2. How can this defect by corrected?

Why does the sky appear blue on a clear day?

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?