Question

An object is placed $6\text{cm}$ in front of a concave mirror. A real image of the same size as the object is obtained. Find out the focal length of the mirror.

• A. $6\text{cm}$
• B. $12\text{cm}$
• C. $1.5\text{cm}$
• D. $3\text{cm}$

Answer 1

The correct option is D $3\text{cm}$

A real image of the same size is formed only when the object is kept at the centre of curvature of the concave mirror.
Therefore, $R=6\text{cm}$
We know, $R=2f$
Hence, $f=3\text{cm}$