Question

A 20 cm long stick is kept in front of a
concave mirror having focal length of 20 cm
in such a way that the end of the stick closest
to the pole is at a distance of 40 cm. What
will be the length of the image?​

Answer 1

Answer:

For end A,

u = - 30 cm

f = - 10 cm

Let the image of the end of the stick at point A has formed at a distance v from the mirror. Therefore, using mirror formula, we have

⇒

f

1

=

v

1

+

u

1

⇒

v

1

=

−10

1

−

−30

1

=−

30

2

v

a

′

=−15 cm

For end B

u = - 20 cm

f = - 10 cm

Let the image of the end of stick at point B is formed at a distance v' from the mirror . Therefor , using mirror formula, we have

f

1

=

v

1

+

u

1

⇒

v

1

=

−10

1

−

−20

1

=−

20

1

⇒v

b

′

=−20cm

Therefore , the length of the image =v

a

′

−v

b

′

=20−15=5 cm