# The image obtained with a convex lens is erect and its length is 4 times the length of the object. If focal length of the lens is 20cm, calculate

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The image obtained with a convex lens is erect and its length is 4 times the length of the object. If focal length of the lens is 20cm, calculate the object and image distances.

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As image formed is erect and hence virtual, the magnification produced by the lens is positive, i.e., m = + 4
f= + 20 cm, u = ?
4 = (20)/(u + 20), 4u + 80 = 20
u = (20 - 80)/(4) = - 15 cm
Again, from m = (f - v)/(f)
4 = (20 -v)/(20)
80 = 20 - v
v = 20 - 80 = - 60 cm