Question

A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is ?​

Answer 1

Answer:

We have,

f

1

=

v

1

+

u

1

Also,

m=

u

v

=

x

−y

Where,

y is image height

and x is object's height.

We have,

x=10 and y=−5

Also, v=30

∴u=60

Now, using mirror's formula:

f

1

=

30

1

+

60

1

∴f=20 cm