Q13 of 13 Page 411

State the function of each of the following parts of the human eye:

(i) Cornea (ii) Iris


(iii) Pupil (iv) Retina


Millions of people of the developing countries are suffering from corneal blindness. The disease can be cured by replacing the defective cornea with the cornea of donated eye. Your school has organized a campaign in the school and its neighborhood in order to create awareness about this fact and motivate people to donate their eyes after death. How can you along with your classmates contribute to this noble cause? State the objectives of organizing such campaigns in schools.


I. CORNEA – The cornea acts as protective layer through which light enters our eye, it is transparent. Most of the refraction occurs here.


II. IRIS – It is dark and behind the cornea. It controls the size of pupil according to the light entering with intensity. It determines eye colour.


III. PUPIL – It checks the amount of light entering the eye and changes it’s size with the help of iris accordingly.


IV. RETINA – The function of retina is to receive the light focused by the eye lens or crystalline lens and convert it to electrical signals that will be interpreted by the brain through optic nerve. It has enormous number of light-sensitive cells.


More from this chapter

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9

An old man cannot see objects closer than 1 m from the eye clearly. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagram for the (i) defect of vision and also(ii) for its correction.

 10

Draw a diagram to show why distant objects cannot be seen distinctly by a myopic eye. List two reasons due to which this defect of vision may be caused.

A person with a myopic eye cannot see objects clearly beyond a distance of 2 m. Name the type of corrective lens that would be needed to correct the defect of vision and draw a ray diagram to show how the defect gets corrected.

 11

With the help of scattering of light, explain the reason for the difference in colours of the sun as it appears during sunrise/sunset and noon.

 12

A narrow beam of light produces a spectrum XY on passing through a triangular glass prism.


(a) State the colour at X and Y.


(b) Why do the different components of white light bend through different angles with respect to the incident beam of light?