Question

Describe the nature of image formed when the object is placed at a distance of 20 cm from a concave mirror of focal length 10 cm.

Answer 1

Object distance (u) = - 20 m ( negative, due to sign convention)
Focal length (f) = -10 m ( negative, due to sign convention)
Image distance = ?
From the mirror formula, we know that:

$\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$

or $\frac{1}{v}+\frac{1}{-20}=\frac{1}{-10}$

$$\begin{gathered} or\frac{1}{v}-\frac{1}{20}=\frac{-1}{10} \\ or\frac{1}{v}=\frac{-1}{10}+\frac{1}{20} \\ or\frac{1}{v}=-\frac{1}{20}orv=-20m \end{gathered}$$

Here, the negative sign means that the image is formed on the left side of the mirror. Thus, it is a real and inverted image, formed at a distance of 20 m from the mirror.