Question

an object of height 1.2mis 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 height of an object formed?

Answer 1

1/u=1/f-1/v
1/u=1/-20-1/-60=-1/30
u= -30
h1/h0=-v/u
h1=-60/-30×-1.2
=-2.4

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 .