A far sighted person has his near point 50 ~cm , find the power of lens he should use to see at 25 ~cm , clearly.

Correct answer: B. +2 D Here u=-25 ~cm, v=-50 ~cm We have (1)/(f)=(1)/(-u)+(1)/(v) i.e, (1)/(f)=(1)/(25)-(1)/(50) or f=50 ~cm Power of lens he should use, P= (100)/(f)=(100)/(50)=+ 2 D

AIIMS 2011

Exam: AIIMS
Year: 2011
Subject: Physics
Chapter: Ray Optics

AIIMS 2011 · Physics · Ray Optics

A far sighted person has his near point 50 ~cm , find the power of...

A far sighted person has his near point

50 \mathrm{~cm}

, find the power of lens he should use to see at

25 \mathrm{~cm}

, clearly.

Options

A $+1 \mathrm{D}$
B $+2 \mathrm{D}$
C $-2 \mathrm{D}$
D $-1 \mathrm{D}$

Correct answer

B. $+2 \mathrm{D}$

Step-by-step solution

Here

u=-25 \mathrm{~cm}, v=-50 \mathrm{~cm}

We have

\frac{1}{f}=\frac{1}{-u}+\frac{1}{v}

i.e,

\frac{1}{f}=\frac{1}{25}-\frac{1}{50} \quad

f=50 \mathrm{~cm}

Power of lens he should use, P=

\frac{100}{f}=\frac{100}{50}=+

\mathrm{D}

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