Q24 of 25 Page 11

(a) A student cannot see clearly a chart hanging on a wall placed at a distance of 3 from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this effect . List its two possible causes.(b) Draw a ray diagram to show how this defect maybe corrected using a lens appropriate focal length.(c) An eye donation camp is being organized by social workers in your locality. and why would you help in this cause? ( CBSE 2013)

(a Myopia is an eye-defect in which a person is unable to see the distant object but can see clearly the nearby objects.


The various causes of myopia are:


1. It is caused due to elongation of eye ball


2. It is caused due to decrease in the focal length of eye lens.


Myopia can be corrected by usage of a concave lens of suitable power.


(b) The Ray diagram which shows the Myopic correction is:




(d) There are millions of people who are blind and can’t see. Camps for eye donation on can help in that as if cornea of the eyes are removed within 6 hours duration of death of a person, then the cornea can be transplanted to the patients who are suffering with corneal blind. If people takes initiatives of donating their eyes, they can save two corneal blind person by donating an eye to each. These camps are to be promoted so that people are encouraged to take the step of eye donation and also awareness should be created regarding it. Moreover, people are required to be made aware about these camps and eye donation by writing slogans, writing poems, skits etc.

More from this chapter

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22

State the cause of dispersion of white light passing through a glass prism. How did Newton show that white light of Sun contains seven colors using two identical glass prisms. Draw a ray diagram to show the path of light when two identical glass prisms are arranged together in inverted position with respect to .each other and a narrow beam of white light is allowed to fall obliquely on one of .the focus of the first prism. ( CBSE 2017, 2016, 2012, 2008)

 23

A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain(i) why the student is unable to see distinctly the objects placed beyond 5 m from his eyes.(ii) the type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens. ( CBSE 2017)

 25

(a) List the parts of the human eye into it. Explain how they perform this function.

(b) Write the function of retina in human eye.


(c) Do you know that the corneal-impairment can be cured by replacing the defective cornea with the cornea of the donated eyes? How and why should we organize groups to motivate the community members to donate their eyes after death? ( CBSE 2009)

 26

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 in old age. What type of lenses are required by the persons suffering from this defect to see the objects clearly?

Akshay, sitting in the last row in his class, could not see clearly the words written 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? ( CBSE 2015)