Question

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

Answer 1

v= -60; f= -20
(1/u)=(1/f)-(1/v) = (1/-20)-(1/-60) = (1/-20)+(1/60) = (-3+1)/60= -2/60 = -1/30
.•.u = -30cm
M= I/O = v/u
.•. I/1.2 = -60/-30
I = 2×1.2 = 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 .