Question

an object of height of 1.2m is placed before a concave mirror of focal length 20 cm. so a real image formed at a distance of 16cm from it. find the position of the object what will be the height of the image

Answer 1

Write down the given and to find first.

h= 1.2m = 120cm, f= -20cm, v = -16cm, u = ? and h' = ?

We know that, 1/f = 1/v + 1/u,

1/-20 = 1/-16 + 1/u

1/u = (1/16) - 1/20

= -(5-4)/80

= -1/80

u = -80cm

h'/h = -v/u

Let h' be x,

x/120 = -16/80

x = -(16×120)/80

= -2×12

h'= -24cm

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 .