Question

Distance between virtual image, which is twice the size of object placed in front of mirror and object is 45 cm. The magnitude of focal length of the mirror is _____cm.

Answer 1

The Correct Answer is : 30

\(|m|=|\frac{v}{u}|=2\)
\(|v|=|2u|\)
n + 2n = 45 
n = 15 cm  
u = –15 
v = 30
\(\frac{1}{v}+\frac{1}{u}=\frac{1}{f}\)
\(\frac{1}{30}+\frac{1}{-15}=\frac{1}{f}\)
\(\frac{1-2}{30}=\frac{-1}{30}=\frac{1}{f}\)
\(⇒ f=30\ cm\)