A concave lens of focal length 15cm forms an image 10cm from the lens. How far is the object placed from the lens? Draw the ray-diagram.
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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}$
$\frac{1}{\text{u}}=-\frac{1}{10}+\frac{1}{15}$
$\frac{1}{\text{u}}=\frac{-2}{60}$
${\text{u}}=-30\text{cm}$
Object is at 30cm fron the concave lens (on left side).
Here, OB = 30cm OF = 15cm OB' = 10cm
$\frac{1}{\text{u}}=-\frac{1}{10}+\frac{1}{15}$
$\frac{1}{\text{u}}=\frac{-2}{60}$
${\text{u}}=-30\text{cm}$
Object is at 30cm fron the concave lens (on left side).
Here, OB = 30cm OF = 15cm OB' = 10cm
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