Question

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

Answer 1

given:-

h=120cm

f= -20cm

v= -60cm

u=? and h'=?

using mirror formula:- 1/v+1/u=1/f

therefore, 1/u=1/f-1/v

= -1/20 - (-1/60)

= -1/20+1/60 = -3+1/60 = -2/60 = -1/30

therefore, 1/u= -1/30

u= -30cm

using magnification formula:-

h'/h= -v/u

therefore, h'= -vxh/u

= 60x120/-30

h'=240cm

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 .