Question

An object at a distance of 30 cm from a
concave mirror gets its image at the same point. The focal length of the mirror is ______.

Options

• - 30 cm

• 30 cm

• - 15 cm

• 15 cm

Answer 1

An object at a distance of 30 cm from a
concave mirror gets its image at the same point. The focal length of the mirror is - 15 cm.

Explanation:

When object is placed at 2F, the image formed by concave mirror is also at 2F.

So, 2F = - 30 or F = - 15 cm.