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

A student sitting on the bench can read the letters written on the blackboard but is not able to read the letters written in his text book.Which of the following statement is correct?

The danger signals installed at the top of tall buildings are red in colour.These can be easily seen from a distance because among all other colours, the red light

The bluish colour of water in deep sea is due to

Which of the following statement is correct?

The sky appears dark instead of blue to an astronaut.State its reason.

What is range of vision?

State one function of iris in human eye.

Why do different colours deviate through different angles on passing through a prism?

State one function of pupil in human eye.

Why do stars twinkle?

Why does the sky appear to be dark instead of blue to an astronaut?

Does myopia or hypermetropia imply necessary that the eye has partially lost its ability of accommodation?If not, what cause these defect of vision?

A person has normal vision, but he cannot distinguish between red-green colour.Why?

Draw ray diagram each showing (i)myopic eye and  (ii) hypermetropic eye.

What is meant by the term 'power of accommodation' of human eye?How does it help a person to see nearby as well as distant object clearly.

(a) What is the meant by the power of accommodation of an eye?
(b)A person with a myopic eye cannot see object beyond 1.2m directly.What should be the type of the corrective lens used? What would be its power

Waht is meant by scattering of light?Use this phenomenon to explain why the clear sky appears blue or the sun appears reddish at sunrise.

(a)List the parts of the human eye that control the amount of light entering into it.Explain how they perform this function.
(b)Write the function of retina human eye.
(c)Do you know that the comeal impairment can be cured by replacing the defective cornea with the cornea of the donated eyes?How and why should we organise groups to motivate the community members to donate their eye after death?