Question

If image formed by both mirror coincide then what is the focal length of convex mirror?

• A. 5 cm
• B. 10 cm
• C. 15 cm
• D. 20 cm

Answer 1

Answer: (A)

Image should be formed $4cm$ behind the mirror
$\Rightarrow \frac{1}{v}+\frac{1}{u}=\frac{1}{f}$
$\Rightarrow \frac{1}{4}+\frac{1}{-20}=\frac{1}{f}$
$\Rightarrow f=5cm$