Question

A convex mirror has a focal length = 20 cm. A convergent beam tending to converge at a point 20 cm behind convex mirror on principal axis falls on it. The image is formed at

• A. Infinity
• B. 40 cm
• C. 20 cm
• D. 10 cm

Answer 1

The correct option is A Infinity

Using mirror formula
$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$
Here we have a virtual object, so the sign of u is positive.

Here $f=+20\text{cm},u=20\text{cm},$
$\frac{1}{v}+\frac{1}{20}=\frac{1}{20}\Rightarrow =\frac{1}{v}=0$
$v=\infty$.