A) + 2 D
B) + 0.50 D
C) - 2 D
D) - 0.5D
Correct Answer: D
Solution :
Distance of vision n = 2 m As the man is unable to see distinctly beyond 2 m. Hence, all the objects placed beyond 2 m (i.e., \[u=\infty \]) must form an image at a distance less or equal to 2 m. The relation for focal length of a lens is \[\frac{1}{f}=\frac{1}{\upsilon }-\frac{1}{u}=\frac{1}{\infty }-\frac{1}{2}=-\frac{1}{2}.\]or\[f=-2m\] Hence, the required power of a lens. \[P=\frac{1}{f}=-\frac{1}{2}=-0.5D\]
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