# A converging mirror form a real image of height 4 cm of an object of height 1 cm paced at 20cm from mirror. Calculate the focal length?

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Converging mirror = concave mirror

h = 1 cm

h' = - 4 cm, as real image => inverted image

m = h'/h = -4/1 = -4

also, m = -v/u = -4 => v = 4 u

1/v + 1/u = 1/f, mirror formula

1/4u + 1/u = 1/f

u = 4f /5

f = 5u/4 = 5/4 * -20 cm = -25 cm.

h = 1 cm

h' = - 4 cm, as real image => inverted image

m = h'/h = -4/1 = -4

also, m = -v/u = -4 => v = 4 u

1/v + 1/u = 1/f, mirror formula

1/4u + 1/u = 1/f

u = 4f /5

f = 5u/4 = 5/4 * -20 cm = -25 cm.