A concave mirror produces three times enlarged image of an object placed at 10cm in front of it. Calculate the focal length of the mirror


The image formed is in front of a concave mirror which is real. Therefore, magnification is negative.

m = -3

u = -10cm

m = \(frac{-v}{u}\)

v = -30

From mirror formula, we know

\(frac{1}{v}+frac{1}{u}=frac{1}{f}\) \(frac{1}{v}+frac{1}{-10}=frac{1}{f}\)

Solving the above equation, we get f = -7.5cm

Therefore, radius of curvature, R = 2f = 15cm.

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