Ray Optics

JEE Main level, single correct, medium

46 of 295

Question 46 of 295

A concave mirror for face viewing has a focal length of 0.4m0.4m. The distance at which you hold the mirror from your face in order to see your image upright with a magnification of 55 is

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Answer: (C) 0.32m0.32m

m=5=−vu⇒v=−5um=5=-\dfrac{v}{u}\Rightarrow v=-5u
f=−0.4mf=-0.4m
From mirror formula,
1v+1u=1f\dfrac{1}{v}+\dfrac{1}{u}=\dfrac{1}{f}
1−5u+1u=1−0.4\dfrac{1}{-5u}+\dfrac{1}{u}=\dfrac{1}{-0.4}
−1+55u=1−0.4\dfrac{-1+5}{5u}=\dfrac{1}{-0.4}
u=45(−0.4)=−0.32mu=\dfrac{4}{5}\left(-0.4\right)=-0.32m
So, distance of object from mirror=0.32m=0.32m

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