An object placed 20cm in front of a mirror is found to have an image 15cm.
- In front of it,
- Behind the mirror.
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- u = -20cm,v = 15cm
$\frac{1}{\text{v}}+\frac{1}{\text{u}}=\frac{1}{\text{f}}$
$\Rightarrow\frac{1}{-15}+\frac{1}{-20}=\frac{1}{\text{f}}$
$\Rightarrow=\frac{1}{\text{f}}=\frac{1}{15}-\frac{1}{20}=\frac{-4-3}{60}=-\frac{7}{60}$
$\therefore\text{f}=-\frac{60}{7}\text{cm}$
The mirror is a concave mirror.
- u = -20cm,v = 15cm
$\frac{1}{\text{v}}+\frac{1}{\text{u}}=\frac{1}{\text{f}}$
$\Rightarrow\frac{1}{15}+\frac{1}{-20}=\frac{1}{\text{f}}$
$\Rightarrow=\frac{1}{\text{f}}=\frac{1}{15}-\frac{1}{20}=\frac{4-3}{60}=-\frac{1}{60}$
$\therefore\text{f}=-{60}\text{cm}$
The mirror is a convex mirror.
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