Question

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

Answer 1

h= 1.2 m
h'=?
image distance(v)=60 cm
object distance (u)=?
focal length (f)= 20 cm

1/f= 1/v-1/u

1/20 = 1/ -60 - 1/u
or, 1/u= 1/-60 - 1/20

or,. 1/u= -4/60
or, u= -60/4
or, u= -15

now,. height of object(h)= 1.2 m
height of image (h') =?
m= h'/h= -v/u
or,. h' = -h * v/u
-120*60/-15
or, -120* -4
-480 cm
or,. -4.8 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 .