Question

al An object is placed 30 cm distance from the concave mirror and
image formed at 12 cm. from the pole. Find the focal length of the
mirror and mention the characteristics of the image formed.​

Answer 1

Explanation:

1/f=1/u-1/v

1/30-1/12

2-5/60

-3/60

1/f=60/-3

=-20cm

Answer 2

Hence the focal length is -20 cm and the image is virtual and erect.

Explanation:

Given data:

• u = 30 cm
• v = 12 cm
• f = ?

Solution:

Focal length can be calculated using mirror's formula such that :

1 / f = 1 / v - 1 / u

1 / f = 1 / -12 - 1 / -30  

f = -20 cm

So, the focal length of the mirror is (-20 cm). The ratio of image distance to the object distance is called magnification of the mirror. It is given by :

m = -v / u

m = -(-12) / 30

m = 0.4

Hence the focal length is -20 cm and the image is virtual and erect.