Question

an object of height 1.2m is placed before a concave mirror of focal length 20cm so that a real images formed at a distance of 60 cm from it find the position of an object what will be the height of the image formed.

Answer 1

Using mirror formula
=>1/f=1/v+1/u
For concave mirror focal length is -ve i.e -20 cm.also,image is formed between 2f and infinity so image distance i.e v is -ve =-60cm.
So, 1/u=1/f-1/v
=>1/u=-1/20-(-1/60)=-1/30
=>u=-30 cm.
Also,I/O=-v/u
=>I=O(-v/u)=1.2m×60/-30=-2.4m
Image is erect and formed in front of mirror and image height=2.4 m

Answer 2

Answer:

u = 30 cm

$\display \text{h _i = 2.4 cm}$

Explanation:

We have given :

Focal length = 20 cm

Image distance =  60 cm

We have to find object distance .

We know :

1 / f = 1 / v + 1 / u

Since image formed is real :

f = - 20 cm and v = - 60 cm

1 / u = 1 - 3 / 60

u = - 30 cm

Hence object distance is 30 cm .

Also given object height = 1.2 cm

We know :

h_i / h_o = - v / u

h_i / 1.2 = - 60 / 20

h_i = - 2.4 cm

Hence image height is 2.4 cm .