Question

# Karan cannot see beyond 5 m. What must be the power (in Dioptre) of the corrective lens to be used by him?- 1- 0.2+ 0.1+ 1

Solution

## The correct option is B - 0.2Since Karan can only see upto 5 m, he is suffering from myopia. This means that, his far point is smaller than the far point of a normal eye, i.e., ∞. Thus, if we keep an object at the normal far point, u=∞, the corrective lens of focal length f must produce an image at his eye’s far point, v= -5 m. From the lens formula, 1v − 1u = 1f = 1f = 1−5 − 1 ∞ P = 1f = −0.2 D   Thus, Karan must use a concave lens of power -0.2 D.

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