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

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

Twinkling of stars is due to atmospheric

The focal length of the eye lens increases when eye muscles

Which of the following statement is correct?

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

Name the type of particles which act as prism in the formation of rainbow in the sky

Give an example of optical phenomena which occurs in nature due to atmospheric refraction.

What is the nature of image formed on the retina?

What is the function of optic nerve in the human eye?

Why do stars twinkle?

How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.

What is the difference in colours of the Sun observed during sunrise/sunset and noon? Give explanation for each

Name the three common defects of vision. What are their causes? Name the type of lens used to correct each of them.

(a)Explain the following terms used in relation to defects in vision and correction provided by them:
(i)Myopia (ii)Astigmatism
(iii)Bifocal lenses (iv)Far-sightedness.
(b)Why is the normal eye unable to focus on an object placed within 10cm from the eye?

(a)Write the function of each of the following parts of human eye:
cornea; iris; crystalline lins;  ciliary muscles
(b)Millions of people of the developing countries of the work are suffering from corneal blindness. These persons can be cured by replacing the defective cornea with the cornea of a donated eye. A charitable society of your city has organised a campaign in your neighbourhood in order to create awareness about this fact. If you are asked to participate in this mission how would you contribute in this noble cause?
(i)State the objective of organising such campaigns.
(ii)List two arguments which you would give to motivate the people to donate their eyes after death.
(iii)List two values which are developed in the persons who actively participate and contribute in such programmes.