Question

Example 10.2
An object, 4.0 cm in size, is placed at 25.0 cm in front of a concare
mirror of focal length 15.0 cm. At what distance from the minu
should a screen be placed in order to obtain a sharp image? Find
the nature and the size of the image.
Solution
​

Answer 1

Answer:

Given:

The size of object = 4.0cm

Distance of the object = 25cm (-ve as it is in front of mirrors)

focal length of concave mirror = 15cm (-ve)

Distance of the image is given by-

v

1

+

u

1

=

f

1

v

1

+

−25

1

=

−15

1

v

1

=

−15

1

+

25

1

=

150

−10+6

150

−4

⇒v=−37.5cm

The screen should be at 37.5cm in front of the lens.

(ii)

The size of the image is given by-

h

0

h

i

=

u

−v

⇒h

i

=

u

−v×h

0

=

−25

−(−37.5)×4

h

i

=−

25

150

=−6cm

The image will be 6cm high and it will be inverted.

(iii)

Refer image 1

The image will be formed at a distance of 37.5cm from the mirror.

It will be an inverted image.