A person who can see things most clearly at a distance of 10 cm, requires spectacles to enable to see clearly thinges at a distance of 30 cm. what should be the focal length of the spectacles ?
Text Solution
Verified by ExpertsThe correct answer is:
A
Since, the person is not able to see distant objects beyond 10 cm so he should use concave lens in his spectacles. Concave lens will form the image of object distant 30 cm, at 10 cm it means.
u = – 30 cm, v = – 10 cm
= 
– 
= 
– 
= – 
or 
= – 
So f = – 15 cm
Minus singe signifies that lens used is concave.
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