A convex lens produces an inverted image magnified three times of an object placed at a distance of 15cm from it. Calculate focal length of the lens.
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m = -3 (Inverted image) u = -15cm$\text{m}=\frac{\text{v}}{\text{u}}$
$-3=\frac{\text{v}}{-15}$
$\text{v}=45\text{cm}$
Lens formula, $\frac{1}{\text{v}}-\frac{1}{\text{u}}=\frac{1}{\text{f}}$$\frac{1}{45}-\frac{1}{-15}=\frac{1}{\text{f}}$
$\frac{1+3}{45}=\frac{1}{\text{f}}$
$\text{f}=\frac{45}{4}\text{cm}$
$\text{f}=11.25\text{cm}$
$-3=\frac{\text{v}}{-15}$
$\text{v}=45\text{cm}$
Lens formula, $\frac{1}{\text{v}}-\frac{1}{\text{u}}=\frac{1}{\text{f}}$$\frac{1}{45}-\frac{1}{-15}=\frac{1}{\text{f}}$
$\frac{1+3}{45}=\frac{1}{\text{f}}$
$\text{f}=\frac{45}{4}\text{cm}$
$\text{f}=11.25\text{cm}$
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