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?
Ciliary muscles present in the human eye enables us to adjust the curvature of the eye lens. This, in turn, changes the focal length of the eye lens.
Presbyopia is the defect in eye which arises because of the gradual weakening of ciliary muscles.
Bifocal lens is used to correct presbyopia.
a) Akshay is not able to see from a far distance, so he is suffering from myopia or nearsightedness.
Myopia can be corrected using a concave lens.
b) The teacher displayed presence of mind and pro-activeness, and she is of considerate nature.
Salman displayed a caring nature, kindness and taught the value of friendship.
c) Akshay can express his gratitude towards the teacher and Salman by thanking them in front of the whole class.
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.
(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.
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.
