Question

A convex lens of focal length ' $f$ ' is placed somewhere in between an object and a screen, the distance between the object and the screen is ' $x$ '. If the numerical value of the magnification produced by the lens is ' $m$ ', then the focal length of the lens is

• A. $\frac{( m +1)^{2} x }{ m }$
• B. $\frac{(m-1)^{2} x}{m}$
• C. $\frac{ mx }{( m +1)^{2}}$
• D. $\frac{m x}{(m-1)^{2}}$

Answer 1

Answer: (C)

$u + v = x$
$m =\frac{ v }{ u }$
$\frac{1}{ v }-\frac{1}{ u }=\frac{1}{ f }$