Question

The focal length of convex lens is $2.5cm$. Its magnifying power for minimum distance of distinct vision will be:

• A. $25$
• B. $52$
• C. $11$
• D. $1.1$

Answer 1

The correct option is C $11$

$f=2.5cm$

$v=-25cm$

$\frac{v}{u}$=?

$u=?$

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

$\frac{1}{2.5}$=$\frac{-1}{25}-\frac{1}{v}$

$\frac{-1}{v}=\frac{10}{25}+\frac{1}{25}$

$\frac{-1}{v}=\frac{11}{25}$

$U=\frac{-25}{11}$

$M=\frac{-v}{u}$

$\Rightarrow$=$\frac{-v}{u}$

$\Rightarrow \frac{-25\times 11}{-25}$

$m=11$