Question

A point object is placed at a distance of 30 cm from a convex mirror of focal length 30 cm. The image will form at

Options

•  infinity

• pole

• focus

• 15 cm behind the mirror.

Answer 1

15 cm behind the mirror
Since u = − 30 cm
v = ?
f = 30 cm

From the mirror formula
\[\frac{1}{u} + \frac{1}{v} = \frac{1}{f}\]
\[or\frac{1}{v} = \frac{1}{f} - \frac{1}{u}\]
\[ \Rightarrow \frac{1}{v} = \frac{1}{30} - \frac{1}{- 30}\]
\[\frac{1}{v} = \frac{1}{30} + \frac{1}{30}\]
\[\frac{1}{v} = \frac{2}{30}\]
\[ \therefore v = 15 \text{ cm }\]