# A concave mirror produces a real image 10 mm tall, of an object 2.5 mm tall placed at 5 cm from the mirror. Calculate focal length of the mirror and t

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A concave mirror produces a real image 10 mm tall, of an object 2.5 mm tall placed at 5 cm from the mirror. Calculate focal length of the mirror and the position of the image?

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Correct Answer - -4cm ; -20cm
Here, h_(2) = - 10 mm, h_(1) = 2.5 mm, u = - 5 cm, f = ? , v = ?
As m = (h_(2))/(h_(1)) = -v/u, (-10)/(2.5) = (-v)/(-5) or v = -20 cm
Negative sign of v shows that image is real.
(1)/(f) = (1)/(v) + 1/u = 1/(-20) - 1/5 = (-1-4)/20 or f = (-20)/5 = -4 cm.