Question

an object is placed 20 cm away from a concave mirror. the image obtained is at a distance of 30 cm on the same side find the focal length of given mirror​

Answer 1

Answer:

answer is 15

Explanation:

Object distance, u=−20 cm

A concave mirror forms a real magnified image only when the image to be formed is inverted i.e. m=−3

Magnification m=

u

−v

∴ −3=

−20

−v

⟹v=−60 cm

Using mirror formula :

v

1

+

u

1

=

f

1

∴

−60

1

+

−20

1

=

f

1

⟹ f=

4

−60

=−15 cm

Thus focal length of the mirror is 15 cm.