A concave lens has focal length 15cm. At what distance should the object from the lens be placed so that it forms an image at 10cm from the lens? Also find the magnification produced by the lens.
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f = -15cm v = -10cm Lens formula, $\frac{1}{\text{v}}-\frac{1}{\text{u}}=\frac{1}{\text{f}}$$\frac{1}{-10}-\frac{1}{\text{u}}=\frac{1}{-15}$
$\frac{1}{\text{u}}=-\frac{1}{10}+\frac{1}{15}$
$\frac{1}{\text{u}}=\frac{-1}{30}$
${\text{u}}=-30\text{cm}$
Object should be placed at a distance of 60cm on the left side of the lens.$\text{m}=\frac{\text{v}}{\text{u}}=\frac{-10}{-30}=+0.33$
$\frac{1}{\text{u}}=-\frac{1}{10}+\frac{1}{15}$
$\frac{1}{\text{u}}=\frac{-1}{30}$
${\text{u}}=-30\text{cm}$
Object should be placed at a distance of 60cm on the left side of the lens.$\text{m}=\frac{\text{v}}{\text{u}}=\frac{-10}{-30}=+0.33$
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