At what distance should an object be placed from a convex lens of focal length 18cm to obtain an image at 24cm from it on the other side? What will be the magnification produced in this case?
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f = 18cm v = 24cmLens formula, $\frac{1}{\text{v}}-\frac{1}{\text{u}}=\frac{1}{\text{f}}$
$\frac{1}{24}-\frac{1}{\text{u}}=\frac{1}{18}$
$\frac{1}{\text{u}}=\frac{1}{24}-\frac{1}{18}$
$\frac{1}{\text{u}}=\frac{3-4}{72}=\frac{-1}{72}$
$\text{u}=-72\text{cm}$
$\text{m}=\frac{\text{v}}{\text{u}}=\frac{24}{-72}=-\frac{1}{3}$
$\frac{1}{24}-\frac{1}{\text{u}}=\frac{1}{18}$
$\frac{1}{\text{u}}=\frac{1}{24}-\frac{1}{18}$
$\frac{1}{\text{u}}=\frac{3-4}{72}=\frac{-1}{72}$
$\text{u}=-72\text{cm}$
$\text{m}=\frac{\text{v}}{\text{u}}=\frac{24}{-72}=-\frac{1}{3}$
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