Question

An object 1.00 cm high is placed 18.0cm from a converging lens forms a real image 2.00cm high. Calculate the focal length of the lens

Answer 1

According to formula of lense,

$\frac{hi}{ho} = \frac{v}{u}$

Here,

h_i = -2

h_o = 1

u = -18

Hence,

$\frac{-2}{1} = \frac{v}{-18}$

v = 36 cm

By lens formula,

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

Hence,

$\frac{1}{f} = \frac{1}{36} + \frac{1}{-18}$

f = -36 cm