A person cannot see distinctly objects kept beyond 2 m. This defectcan be corrected by using a lens of power(a) + 0.5 D(b) – 0.5 D(c) + 0.2 D(d) – 0.2 D
Question
A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power
(a) + 0.5 D
(b) – 0.5 D
(c) + 0.2 D
(d) – 0.2 D
Solution
The person is suffering from myopia or nearsightedness, a condition where the person can see nearby objects clearly but distant objects appear blurry.
To correct this defect, we need a diverging or concave lens. The power of the lens is given by the formula:
P = 1/f
Where: P = power of the lens f = focal length of the lens
The person cannot see objects beyond 2 m clearly, so the focal length needed is -2 m (negative because it's a diverging lens).
Substituting the value in the formula, we get:
P = 1/(-2) = -0.5 D
So, the correct option is (b) -0.5 D.
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