Question

A object of height 1.2m is placed before a concave mirror of focal length 20cm so that the image is real image is formed ar a distance of 60cm .find the position and what will be the height of images l

Answer 1

Given.......

Mirror = concave

F = -20cm (negative in concave)

V = -60 (negative in concave)

therefore position of the object (u) is..

MIRROR FORMULA...

$\frac{1}{f} = \frac{1}{v} + \frac{1}{u} \\ \\ \frac{1}{ - 20} - \frac{1}{ - 60} = \frac{1}{u} \\ \\ \frac{ - 3 + 1}{60} = \frac{1}{f} \\ \\ \frac{ - 2}{60} = \frac{1}{u} \\ \\ \frac{ - 1}{30} = \frac{1}{u} \\ \\ u = - 30 \\ \\ now \: height \: of \: the \: object \: is \: 1.2m \: = 120cm \\ \\ there \: \frac{h1}{h2} = \frac{ - v}{u} \\ \\ \frac{120cm}{h2} = \frac { - ( - 60cm)}{ - 30cm} \\ \\ \frac{120cm}{h2} = \frac{2cm}{ - 1cm} \\ \\ cross \: multiply \\ \\ 2h2 cm= - 120cm \\ \\ h2 = \frac{ - 120cm}{2} \\ \\ h2 = - 60cm \\ \\ therefore \: height \: of \: the \: image \: is \: - 60cm \\ \\ \\ \\ hope \: helps$

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 .