Question

when a bright object is placed 10 cm away from a concave mirror its real image is formed at a distance of 40 cm from the mirror what is the focal length of the mirror

Answer 1

Answer:

-8 cm will be the answer

Explanation:

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Answer 2

Answer:

The focal length of the mirror -8 cm.

Explanation:

Given:

when an object exists placed $10$ cm away from a concave mirror its real image exists formed at a distance of $40$ cm from the mirror.

To find:

the focal length of the mirror.

Focal length

The space between the convex lens or a concave mirror and the focal point of a lens or mirror exists named the focal length. It exists at the point where parallel beams of light meet or converge.

$\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$

$\Rightarrow\frac{1}{f}=\frac{1}{(-40)}+\frac{1}{(-10)}$

$\Rightarrow\frac{1}{f}=\frac{-1+(-4)}{40}$

$\Rightarrow \frac{1}{f}=-\frac{81}{408}$

$\Rightarrow \frac{1}{f}=-\frac{1}{8}$

$\Rightarrow f=-8$

$f$ focal length

$=-8 \mathrm{~cm}$

Therefore, the focal length of the mirror -8 cm.

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