Question

A)Two converging lenses, each of focal length 13.1 cm, are placed 58.6 cm apart, and an object is placed 29.9 cm in front of the first. Where is the final image relative to the second lens formed?

B)What is the magnification of the system?

Answer 1

Since the left lens is placed at 58.6 cm to the left of the right lens. If i place the object at 29.9 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/(1/13.1 - 1/29.9) = 23.315 cm

q is '+', => the image is real and situated 23.315 cm to the right of the left lens.

This real image becomes the object of the second lens.

So for the right lens p = 58.6-23.315 =35.285cm, then q is:

q = 1 / (1/13.1 - 1/35.285) = 20.835 cm

q is '+' so the image is real

.B)Magnification:

M = (q/p)(q/p)' = (23.315/30)(20.835/35.285) = -0.459