Question

A convex lens of focal length produces a real image x times the size of an object, then the distance of the object from the lens is

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

Answer 1

The correct option is C $\left(\frac{x+1}{x}\right)f$

$M=\frac{-\vartheta }{u}=\frac{-x}{1}$

$\vartheta =-xu$

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

$\frac{1}{xu}+\frac{1}{u}=\frac{-1}{f}$

$\frac{(1+x)}{xu}=\frac{-1}{f}$

$u=\frac{(1+x)}{\left(x\right)}f$