a)
The function of:
Cornea: When light enters the eye, most of the refraction occurs at the surface of cornea.
Iris: It is a dark, muscular diaphragm that controls the size of the pupil.
Crystalline lens: Helps in the finer adjustment of the focal length required to focus objects at different distances on the retina.
Ciliary muscles: The lens becomes thin when ciliary muscles are relaxed thereby, increasing its focal length. Thus, we are able to see the distant object clearly. The ciliary muscles contract, when we are viewing objects nearby, increasing the curvature of the eye lens. Therefore, the eye lens becomes thicker and focal length decreases. This makes it easier to see the nearby objects clearly.
b)
i) The objective of such organisation is to light up the life of a blind person by donating eyes. the objective statement will be, 'Enlighten the life of Blind'.
ii) The arguments are:
1. We have enjoyed our life by seeing the beauty of nature. Then why not give the same pleasure to the blind. Pass on your gift of vision to the needy and do a charitable deed.
2. Age group of a person or sex does not matter when it comes to donating eyes. If a person uses spectacles or underwent surgery for cataract, can also donate eyes. A person suffering from any kind of communicable disease cannot donate eyes.
iii) Social welfare, awareness, charitability are some of the values that is developed in a person who actively participate and contribute to such programs.
A student is unable to see clearly the words written on the blackboard placed at a distance of approximately 4 m from him. Name the defect of vision the boy is suffering from. Explain the method of correcting this defect. Draw ray diagram for the:
(i) defect of vision and also
(ii) for its correction.
(a) A person cannot read newspaper placed nearer than 50 cm from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length.
(b) We see advertisements for eye donation on television or in newspapers. Write the importance of such advertisements.
What is atmospheric refraction? Use this phenomenon to explain the following natural events:
a) Twinkling of stars
b) Advanced sunrise and delayed sunset
Draw diagrams to illustrate your answer.
Write the importance of ciliary muscles in the human eye. Name the defect of vision that arises due to gradual weakening of the ciliary muscles. What types of lenses are required by the person suffering from this defect to see the objects clearly?
Akshay, sitting in the last row in his class, could not see clearly the words write on the blackboard. When the teacher noticed it, he announced if any student sitting in the front row could volunteer to exchange his seat with Akshay. Salman immediately agreed to exchange his seat with Akshay. He could now see the words written on the blackboard clearly. The teacher thought it fit to send the message to Akshay’s parents advising them to get his eyesight checked.
In the context of the above event, answer the following questions:
(a) Which defect of vision is Akshay suffering from? Which type of lens is used to correct this defect?
(b) State the values displayed by the teacher and Salman.
(c) In your opinion, in what way can Akshay express his gratitude towards the teacher and Salman?
