Question

A point object is placed at a distance of 20 cm from a convex mirror of focal length 20 cm. The image will form at:-
(a) at infinity
(b) at focus
(c) at the pole
(d) behind the mirror

Answer 1

Answer:

Behind the mirror (v = 10cm)

Explanation:

u = -20cm

f = 20cm

1/f = 1/v + 1/u

1/20 = 1/v + 1/(-20)

2/20 = 1/v

v= 10cm

As v is positive means it will form behind the mirror.

Answer 2

Answer:

The image is formed behind the mirror. Option (d) is correct.

Explanation:

• The reflected light ray from a convex mirror appears as if it is coming in a diverging manner from a point that is behind the mirror.
• In vehicles, convex mirrors are used for rear viewing.
• Only virtual images are formed by convex mirrors.

The mirror formula is:

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

where $v$ is the image distance

           $u$ is the object distance.

           $f$ is the focal length.

Step 1:

The convex mirror's focal length, $f=20$ $cm$

The object distance, $u=-20$ $cm$

When we apply the mirror formula:

Step 2:

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

$\frac{1}{v}=\frac{2}{20}$

$v=10$ $cm$

So, the image is formed behind the mirror (due to the positive image distance).

Hence, option (d) is correct.