Question

U size.
15. Ano
An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal
length 18 cm. At what distance from the mirror should a screen be placed, so that
a sharp focussed image can be obtained? Find the size and the nature of the image.
16 Pb​

Answer 1

Answer:

Here, Object distance, u = -27 cm (To the left side of mirror)

Image distance, v = ? (To be calculated)

Focal length, f = -18 cm (It is a concave mirror)

Height of object, h1 = 7.0 cm

 And, Height of image, h2 = ? (To be calculated)

Now, For a mirror:  

1/v + 1/u = 1/f

1/v + 1/-27 = 1/-18

= 1/-18 + 1/27

= -3+2/54

Image distance, v = -54 cm

Since the image distance is minus 54 cm, therefore, the screen should be placed at a distance of 54 cm in front of the concave mirror (on its left side). The nature of image obtained on the screen is real and inverted.

Also, For a mirror,  

h2/h1 = -v/u

h2/7.0 = -(-54)/-27

h2/7.0 = -2

h2 = -2*7.0

= -14.0 cm

Thus, the size of image is 14.0 cm.

Hope it helps you.