Q23 of 25 Page 11

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)

Two possible reasons are lengthening of eye ball from front to back or lens have become too curved.

i. The rays coming from an object placed beyond 5 m from his eyes forms the image in front of the retina.



ii. Concave lens diverges the light rays coming from the object, thus the image is formed at the retina. Hence by using concave lens a person suffering from myopia can see distant objects.


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An old man cannot see objects closer than 1 m from the eye clearly. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagram for the (i) defect of vision and also(ii) for its correction. ( CBSE 2009)

 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)

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(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)