Q26 of 25 Page 11

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) 

Ciliary muscles is important because they helps in modifying the curvature of eye lens so that eye can focus objects which are at varying distances. The focal length is changed by contraction and relaxation of ciliary muscles. We are able to see nearby and also the distant object clearly by using bifocal lenses which consists of both concave and convex lens. The upper part of lens is Concave lens which is used for distant vision and the lower part of lens is convex lens which is for nearby objects. Bifocal lens are used in Presbyopia condition when the person can’t see distant as well as nearby objects.


(a) Akshay is suffering from Myopia defect in which the person can’t see distant objects clearly. Concave lens of suitable power is used to correct it.


(b) The teacher showed concerned and care towards the health of Akshay. Moreover, Salman has also showed helping and caring nature.


(c) Akshay should thank his teacher as well as Salman for the caring nature they showed towards him.

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)

 24

(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)

 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)