Advertisements
Advertisements
Question
The near point of the eye of a person is 50 cm. Find the nature and power of the corrective lens required by the person to enable him to see clearly the objects placed at 25 cm from the eye?
Advertisements
Solution
Given:
Object distance (u) = −25cm
Image distance (v) = −50cm
Focal length, f = ?
Using the lens formula
`1/"f" = 1/"v" - 1/"u"`
`1/"f" = 1/(-50) - 1/(-25)`
`1/"f" = -1/50 + 1/25`
`1/"f" = (-1+2)/50`
`1/"f" = 1/50`
`"f"` = 50 cm
Since the focal length of the lens is positive, the corrective lens required is a convex lens.
`"f"` = 50cm
`"f"` = 0.5m
Power (P) of the corrective lens will be
`"P" = 1/("f"("m"))`
`"P" = 1/0.5`
`"P" = + 2 "D"`
APPEARS IN
RELATED QUESTIONS
A student is unable to see clearly the words written on the blackboard placed at a distance of approximately 4 m from him. Name the defect of vision the boy is suffering from. Explain the method of correcting this defect.
Draw ray diagram for the:-
(i) defect of vision and also
(ii) for its correction.
List three common refractive defects of vision. Suggest the way of correcting these defects.
A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.
Name the defect of vision in which the eye-lens loses its power of accommodation due to old age.
Explain with the help of labelled ray-diagram, the defect of vision called hypermetropia, and hot it is corrected by a lens.
A young man has to hold a book at arm's length to be able to read it clearly. The defect of vision is:
(a) astigmatism
(b) myopia
(c) presbyopia
(d) hypermetropia
Differentiate between:
Myopia and Hypermetropia.
Explain the Term: Cataract
Name the following:
The defect of the human eye caused due to the uneven surface of the cornea.
Match the following:
| Column - I | Column - II |
| 1. Retina | a. Path way of light |
| 2. Pupil | b. Far point comes closer |
| 3. Ciliary muscles | c. near point moves away |
| 4. Myopia | d. Screen of the eye |
| 5. Hypermetropia | e. Power of accommodation |
