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Question
A man cannot see beyond a distance which is 10 times the least distance of distinct vision of a normal human-eye. This defect is corrected by using a lens of power:
A man cannot see beyond a distance which is 10 times the least distance of distinct vision of a normal human-eye. This defect is corrected by using a lens of power:
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Solution
The correct option is B -0.4 D
The least distance of distinct vision for a young adult with normal vision is = 25 cm
It means this person cannot see beyond the distance:
d = 10 x 25 cm
d = 250 cm
d = 2.5 m
So, he is suffering from Myopia which is corrected using a concave lens. For objects at infinity of concave lens, image is formed at focus. So, if the focal point is same as his far point (2.5 m), his defect will be rectified. Power of the lens required is: P = 1/f
= 1/(-2.5)
= -0.4 D
The least distance of distinct vision for a young adult with normal vision is = 25 cm
It means this person cannot see beyond the distance:
d = 10 x 25 cm
d = 250 cm
d = 2.5 m
So, he is suffering from Myopia which is corrected using a concave lens. For objects at infinity of concave lens, image is formed at focus. So, if the focal point is same as his far point (2.5 m), his defect will be rectified. Power of the lens required is: P = 1/f
= 1/(-2.5)
= -0.4 D
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