Question

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

Answer 1

h1=1.2m.....120cm
f=-20cm
v=-60cm
U=?
h2=?

1/f=1/v+1/u
1/-20=1/-60+1/u
1/-20+1/60=1/u
(-3+1)/60=1/u
-2/60=1/u
-60/2=u
-30=u

U(the position of the object)=-30cm

to get the height of image,
use formula
h2/h1=-v/u
h2/120=-(-60)/-30
h2\120=60/-30
h2/120=-2
h2=-240

The height of the object's image=-240cm

...... Hope this helps you..........

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 .