Question

an object is placed 30 cm in front of a concave mirror and a real image is formed at 15 cm from the mirror. what is the focal length of the mirror

Answer 1

Answer:

1/f= 1/v +1/u

is the mirror formula and in concave mirror the image and object is taken negative

Answer 2

An object is placed 30 cm in front of a concave mirror and a real image is formed at 15 cm from the mirror. The focal length of the mirror is 10 cm

Explanation:

Given:

Distance of the object $u=30$ cm

Distance of the image $v=15$ cm

To find:

Focal length of the mirror $f$

Formula used:

Mirror formula

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

Since the mirror is concave mirror and image formed is real image

Therefore, the object and image distance will have same sign

Therefore, using the mirror formula

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

$\implies\frac{1}{15}+\frac{1}{30}=\frac{1}{f}$

$\implies\frac{1}{f}=\frac{2+1}{30}$

$\implies \frac{1}{f}=\frac{3}{30}$

$\implies \frac{1}{f}=\frac{1}{10}$

$\implies f=10$ cm

Hope this answer is helpful.

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