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.
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u = -15cm, v = -10cm f = ? We know that$\frac{1}{\text{v}}+\frac{1}{\text{u}}=\frac{1}{\text{f}}$
$\Rightarrow\frac{1}{(-10)}+\frac{1}{(-15)}=\frac{1}{\text{f}}$
$\Rightarrow\frac{1}{\text{f}}=\frac{1}{10}-\frac{1}{15}= \frac{-3-2}{30}=-\frac{5}{30}=-\frac{1}{6}$
$\therefore \text{f}=-6\text{cm}$
$\therefore $ The focal length of the concave mirror is 6cm.
$\Rightarrow\frac{1}{(-10)}+\frac{1}{(-15)}=\frac{1}{\text{f}}$
$\Rightarrow\frac{1}{\text{f}}=\frac{1}{10}-\frac{1}{15}= \frac{-3-2}{30}=-\frac{5}{30}=-\frac{1}{6}$
$\therefore \text{f}=-6\text{cm}$
$\therefore $ The focal length of the concave mirror is 6cm.
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