Question
A concave lens has a focal length 15 cm. If the object
is placed at 30 cm from the lens, what is the image distance?Solution
focal length f = -15 cm Distance of object u = -30 cm 1/ v = 1/f +1/u substituting these values in the lens equation we get, 1/v =1/-15 +1/-30 1/v =-3/30 v = -10cm Hence, the distance of the object from the lens is 10 cm and the negative sign signifies a virtual image.
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