Question

A convex lens of focal length f produces a real image $x$ times the size of an object then what will be the distance of the object from the lens?

• A. $\left(\right(x+1\left)/x\right)2f$
• B. $\left(\right(x+1\left)/2x\right)f$
• C. $\left(\right(2x+1\left)/x\right)f$
• D. $\left(\right(x+1\left)/x\right)f$

Answer 1

The correct option is D $\left(\right(x+1\left)/x\right)f$

For real image,

$m=\frac{v}{u}=-x\left(given\right)So,v=-xu\text{From lens formula}\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\Rightarrow \frac{1}{-xu}-\frac{1}{u}=\frac{1}{f}\Rightarrow u=-\frac{(x+1)}{x}f\text{So, object should be placed at a distance}\frac{(x+1)}{x}f,\text{from the lens.}$