(a)What is meant by the term ‘power of accommodation’? Name the component of eye that is responsible for the power of accommodation.
(b) A student sitting at the back bench in a class has difficulty in reading. What could be his defect of vision? Draw ray diagrams to illustrate the image formation of the blackboard when he is seated at the (i) back seat (ii) front seat. State two possible causes of this defect. Explain the method of correcting this defect with the help of a ray diagram.
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a) The ability of eye lens to adjust its focal length so as to clearly focus image on the retina of the object situated in front of the eye.
Ciliary Muscle is responsible for the power of Accommodation.
b) The student is suffering from Myopia.
i) For back seat - The ray diagram is given in the Science NCERT Book, page number - 189. Fig. (b)
ii) For front seat - Fig. (a)
[CAUSES OF MYOPIA]
1) Either the power of eye lens has become more than its normal value, or
2) Elongation of eye ball due to some genetic defect.
[FOR CORRECTING THIS DEFECT]
A concave lens of appropriate focal length is used.
For diagram, P - 189. Fig. (c)
☺
Ciliary Muscle is responsible for the power of Accommodation.
b) The student is suffering from Myopia.
i) For back seat - The ray diagram is given in the Science NCERT Book, page number - 189. Fig. (b)
ii) For front seat - Fig. (a)
[CAUSES OF MYOPIA]
1) Either the power of eye lens has become more than its normal value, or
2) Elongation of eye ball due to some genetic defect.
[FOR CORRECTING THIS DEFECT]
A concave lens of appropriate focal length is used.
For diagram, P - 189. Fig. (c)
☺
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