A concave mirror forms a sharp image of an object on a screen in front of the mirror

PHYSICS · Subjective · CBSE · Physics · Light — Reflection and Refraction · Light — Reflection and Refraction

Problem

A concave mirror forms a sharp image of an object on a screen

60\,\text{cm}

in front of the mirror. When the object is moved

20\,\text{cm}

closer to the mirror, the screen has to be shifted

30\,\text{cm}

farther away to obtain a sharp image again. Determine the focal length of the mirror.