Question

An object is placed at a distance of 10 cm from a concave mirror of focal length 20 cm.

(a) Draw a ray diagram for the formation of image.
(b) Calculate the image distance.
(c) State two characteristics of the image formed.

Answer 1

(a) Ray Diagram-

(b) Image Distance-

Distance of the object from the mirror 'u' = −10 cm
Focal length of the concave mirror 'f' = −20 cm

We have to find the distance of the image 'v'.

Mirror Formula:
$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$
Therefore

$$\begin{gathered} \frac{1}{-20}=\frac{1}{v}+\frac{1}{-10} \\ \frac{1}{v}=-\frac{1}{20}+\frac{1}{10}=-\frac{1}{20}+\frac{2}{20} \\ \frac{1}{v}=\frac{1}{20} \\ v=20\mathrm{cm} \end{gathered}$$

Thus, the distance of the image 'v' is 20 cm.

(c) Two characteristics of the image formed is as follows:

(1) It is virtual and erect.

(2) It is magnified.