Question

Rays from the sun converges at a point $15\text{cm}$ in front of a concave mirror. Where should be the object must be placed so that the size of its image is equal to the size of the object?

• A. $15\text{cm}$ in front of the mirror
• B. $30\text{cm}$ in front of the mirror
• C. Between $15\text{cm}$ and $30\text{cm}$ in front of the mirror
• D. More than $30\text{cm}$ in front of the mirror

Answer 1

The correct option is B $30\text{cm}$ in front of the mirror

Light rays from the sun after reflection from the concave mirror will converge at the focus.
So, here $f=15cm$
Also, for a concave mirror, the image size becomes equal to the object size when the object distance is equal to the radius of Curvature of the mirror.
$\Rightarrow u=R=2f$
$\therefore u=30\text{cm}$