Question

A convex lens of focal length $f$ produces a real image $\mu$ times the size of an object, Then what is the distance of the object from the lens?

• A. $(\mu -1)f$
• B. $(\mu +1)f$
• C. $\frac{(\mu -1)f}{\mu }$
• D. $\frac{(\mu +1)f}{\mu }$

Answer 1

Answer: (D)

$\frac{(\mu +1)f}{\mu }$

Since image formed is real , so magnification will be negative.

Magnification $m=-\mu$ $,-\mu =\frac{v}{u}$ $,\mu =\frac{-v}{u}$

$\Rightarrow v=-u\left(\mu \right)$

Lens formula, $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

$\Rightarrow \frac{-1}{u\left(\mu \right)}-\frac{1}{u}=\frac{1}{f}$

$\Rightarrow u=\frac{f(\mu +1)}{\mu }$

Hence, the answer is $\frac{f(\mu +1)}{\mu }.$