Question

An object placed at 60 CM in front of concave mirror makes an image 30 cm in front of mirror. then what is distance of the focus of the mirror.​

Answer 1

u = -60 cm

v = -30 cm

using mirror formula

$\frac{1}{f} = \frac{1}{v} + \frac{1}{u} \\ \\ \frac{1}{f} = \frac{1}{ - 30} + \frac{1}{ - 60} \\ \\ \frac{1}{f} = \frac{ 2 + 1}{ - 60} \\ \\ \frac{1}{f} = \frac{3}{ - 60} \\ \\ f = \frac{ - 60}{3} \\ \\ f = - 20 \: cm$