Two converging lenses, each of focal length 14.9 cm, are placed 39.6 cm apart, a
ID: 2012044 • Letter: T
Question
Two converging lenses, each of focal length 14.9 cm, are placed 39.6 cm apart, and an object is placed 30.0 cm in front of the first lens. Where is the final image formed?The image is located?
What is the magnification of the system?
M =
Explanation / Answer
Since the left lens is placed at 39.6 cm to the left of the right lens. If i place the object at 30 cm in front of this lens I can find the image distance using 1/f=1/p+1/q; q = 1 / (1/f - 1/p) = 1/(1/14.9 - 1/30) = +29.6 cm q is '+', => the image is real and situated 29.6 cm to the right of the left lens. This real image becomes the object of the second lens. So for the right lens p = 39.6 - 29.6 = 10 cm, then q is: q = 1 / (1/14.9 - 1/10) = -30.41 cm q is '-' so the image is virtual .Magnification: M = (q/p)(q/p)' = (29.6/30)(30.41/10) = 3