A convex lens has focal length of 30 cm . Calculate at what distance should the object be placed from the lens so that it forms an image at 60 cm on the other side of the lens ? FIND THE MAGNIFICATION PRODUCED BY THE LENS IN THIS CASE.
Answers
Concept:
The lens formula for convex lens is given as, 1/f = 1/v - 1/u
Given:
Focal length of convex lens, f = 30 cm
Image distance, v = 60 cm
Find:
a. We need to determine the distance should the object be placed from the lens so that it forms an image at 60 cm on the other side of the lens.
b. The magnification produced by the lens?
Solution:
We know, the lens formula as, 1/f = 1/v - 1/u where f is the focal length, v is the image distance and u is the object distance.
Therefore, 1/u = 1/v - 1/f
1/u = 1/60 - 1/30
1/u = 1-2/60 = -1/60
Therefore, u = -60 cm is the distance should the object be placed from the lens so that it forms an image at 60 cm on the other side of the lens.
Magnification of a lens is given by, m = h2/h1 = v/u
Therefore, m = 60/-60
m = -1 ( negative sign indicates that the image formed is inverted)
Thus, the distance should the object be placed from the lens so that it forms an image at 60 cm on the other side of the lens is - 60cm and the magnification produced by the lens is -1.
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