Question

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

Answer 1

v=-60
f=-20
we know
1/ f=1/v+1/u
1/u=1/-30
u=-30
we know
hi/ho=-v/u
hi/1.2=-(-60)/-30
hi/1.2=-2
hi=-2.4
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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 .