Question

An object is kept 10cm infront of concave mirror and and its real image is formed of 30cm apart. Find the focal length of mirror.​

Answer 1

Answer:

Focal length of the mirror is 15 cm

Given

An object is kept 10 cm infront of concave mirror and and its real image is formed of 30 cm apart

To Find

Focal length of mirror

Formula Used

Mirror Formula

\bullet \rm \;\;\; \dfrac{1}{f}=\dfrac{1}{u}+\dfrac{1}{v}∙

f

1

=

u

1

+

v

1

Solution

Object distance , u = - 10 cm

Image distance , v = 30 cm

Focal length , f = - ? cm

Apply mirror formula

\begin{gathered}\implies \rm \dfrac{1}{f}=\dfrac{1}{u}+\dfrac{1}{v}\\\\\implies \rm \dfrac{1}{-f}=\dfrac{1}{-10}+\dfrac{1}{30}\\\\\implies \rm \dfrac{1}{-f}=\dfrac{30-10}{-300}\\\\\implies \rm \dfrac{1}{-f}=\dfrac{20}{-300}\\\\\implies \rm \dfrac{1}{-f}=\dfrac{2}{-30}\\\\\implies \rm \dfrac{1}{-f}=\dfrac{1}{-15}\\\\\implies \rm -f=-15\ cm\\\\\implies \rm f=15\ cm\end{gathered}

⟹

f

1

=

u

1

+

v

1

⟹

−f

1

=

−10

1

+

30

1

⟹

−f

1

=

−300

30−10

⟹

−f

1

=

−300

20

⟹

−f

1

=

−30

2

⟹

−f

1

=

−15

1

⟹−f=−15 cm

⟹f=15 cm

Answer 2

hope its helpful for you