Question

when an object is placed at a distance of 15cm from a concave mirror, its image is formed at 10cm in front of the mirror.calculate the focal length of the mirror​

Answer 1

$\huge\star\underline\green{Answer:-}$

Given

Object distance u= 15 cm

Image distance v=10 cm

Let f be the focal length.

we know

$\frac{1}{f} = \frac{1}{u} + \frac{1}{v} \\ = \frac{1}{15} + \frac{1}{10} \\ = \frac{2 + 3}{30} \\ = \frac{5}{30} \\ = \frac{1}{6} \\ \frac{1}{f} = \frac{1}{6} \\ f = 6cm$

Hence the focal length is 6 cm.

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Regards,

Abhinay.

Answer 2

Answer: f = -6cm

Explanation: Using mirror formula

f = uv/u+v

f = -10 x -15/-10 + -15

f = -150/25 = -6cm

Note : the focal length of a concave mirror is always negative