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प्रश्न
A short-sighted person has a near point of 15 cm and a far point of 40 cm.
(a) Can he see clearly an object at a distance of:
(i) 5 cm?
(ii) 25 cm?
(iii) 50 cm?
(b) To see clearly an object at infinity, what kind of spectacle lenses does he need?
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उत्तर
a) (i) A short-sighted person with a near point of 15 cm and a far point of 40 cm in front of the eye cannot clearly see an object at a distance of 5 cm because he can see an object only when it is placed at his near point (i.e., 15 cm).
(b) A short-sighted person can clearly see an object at a distance of 25 cm as it the normal near point of the eye. Moreover, the person's far point is located at 40 cm from the eye.
(c) The person cannot see the object clearly as it is at a distance of 50 cm, which is beyond his far point.
(d) In order to see an object clearly at infinity, the person should use concave lenses in his spectacles. A concave lens first diverges the light rays from the object at infinity to form a virtual image at the eye's far point. The eye lens then easily focusses the rays from the eye's far point to form a clear image on the retina.
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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.
(b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention
Name the defect of vision in a person:
whose near point is more than 25 on away.
What is the other name for
myopia
Name the defect of vision which can be corrected by a diverging lens. Show clearly by a ray diagram how the lens corrects the defect.
The defect of vision which cannot be corrected by using spectacles is:
(a) myopia
(b) presbyopia
(c) cataract
(d) hypermetropia
Given below is a diagram depicting a defect of the human eye. Study the same and answer the question that follow:
Name the defect shown in the diagram.
A student cannot see a chart hanging on a wall placed at a distance of 3 m from him. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagrams for the (i) defect of vision and also (ii) for its correction.
What is Hypermetropia (far sightedness)?
Given alongside is a diagram depicting a defect of the human eye. Study the same and then answer the questions that follow:
(i) Identify the defect.
(ii) Name the parts labelled 1, 2 and 3.
(iii) Give labelled two possible reasons for this eye defect.
(iv) Draw a labelled diagram to show how the above mentioned defect is rectified.
A person is unable to see objects distinctly placed within 50 cm from his eyes.
(a) Name the defect of vision the person is suffering from and list its two possible causes.
(b) Draw a ray diagram to show the defect in the above case.
(c) Mention the type of lens used by him for the correction of the defect and calculate its power. Assume that the near point for the normal eye is 25 cm.
(d) Draw a labeled diagram for the correction of the defect in the above case.
Name an old age eye defect. Why is it caused?
Give Reason:
Older people require glasses to read and write.
Give Technical Term:
The path which responsible for protecting the eye from sweat.
Study the following diagram carefully and then answer the questions that follow. The diagram is depicting a defect of the human eye :
(i) Identify the defect shown in the diagram.
(ii) Give two possible reasons for the above defect.
In Myopia the human eye _______.
Assertion: Myopia is the defect of vision in which a person cannot see distant objects clearly.
Reason: This due to eye-ball being too short.
Observe the figure whether it is correct or not and explain the phenomenon.
Name the following:
Two kinds of accomodations.
