Question

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

Answer 1

h1 = 120 cm
v = -60 cm
f = -20 cm
u = ?
use the formula 1/v + 1/u = 1/f
magnification = - v/u eq. 1
magnification = h1/ h2 eq.2

Answer 2

Answer:

u = 30 cm

$\display \text{h _i = 2.4 m}$

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 m

We know :

h_i / h_o = - v / u

h_i / 1.2 = - 60 / 20

h_i = - 2.4 m

Hence image height is 2.4 m .