Question

2. A real image, 1/5 th size of object is formed at a distance of 18 cm from
a mirror, What is the nature of the mirror ? Calculate its focal length,​

Answer 1

Answer:

Given: a real image is

5

1

th

the size of the object, and it is formed at a distance of 18cm from the mirror.

To find the focal length of the mirror and the nature of the mirror.

Solution:

According to the given criteria,

image distance, v=−18cm

magnification, m=−

5

1

as the image formed is real hence it will be inverted.

We know,

m=−

u

v

⟹−

5

1

=−(

u

−18

)

⟹u=−(5×18)=−90cm

Applying the lens formula,

f

1

=

v

1

+

u

1

⟹

f

1

=

−18

1

+

−90

1

⟹

f

1

=

90

−5−1

⟹f=−15cm

Answer 2

Answer:

Real image means the mirror is a concave mirror.