Question

An object is placed at a distance of 10cm from a concave mirror of focal length 20cm

A. Calculate the image distance

Answer 1

$\huge{\star}{\underline{\boxed{\red{\sf{Answer :}}}}}{\star}$

Concave Mirror

Object distance (u) = -10 cm

Focal length (f) = -20 cm

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We have to find image distance (v)

Put value in formula :-

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

$\LARGE{\sf{\frac{1}{v} \: = \: \frac{1}{f} \: - \: \frac{1}{u}}}$

______________[Put Values]

$\LARGE{\sf{\frac{1}{v} \: = \: \frac{1}{-20} \: - \: \frac{1}{-10}}}$

$\LARGE{\sf{\frac{1}{v} \: = \: \frac{1}{-20} \: + \: \frac{1}{10}}}$

$\LARGE{\sf{\frac{1}{v} \: = \: \frac{-1 \: + \: 2}{20}}}$

$\LARGE{\sf{\frac{1}{v} \: = \: \frac{1}{20}}}$

$\huge{\implies}{\boxed{\boxed{\red{\sf{v \: = \: 20 \: cm}}}}}$

•°• Image distance is 20 cm

Answer 2

$\mathfrak{Answer}$

$\mathcal{Given:}$

Object distance, u = -10 cm

Focal length, f = -20 cm

$\mathcal{Solution:}$

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

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

$\frac{1}{v} = \frac{1}{ - 20} - \frac{1}{ - 10}$

$\frac{1}{v} = - \frac{1}{20} + \frac{1}{10}$

$\frac{1}{v} = \frac{ - 10 + 20}{200}$

$\frac{1}{v} = \frac{10}{200}$

$\frac{1}{v} = \frac{1}{20}$

$v = 20 \: cm$