Hint (Hwk#3, Pb 7)

In homework #3, problem #7, it asks you to show that the magnification is unchanged between the 2 situations:
- either using only L1
- or using the combination of L1 and L2, with L2 located at the focal point of L1.

Now, what the problem does not tell you is: (i) which focal point of L1 the second lens is located at, and (ii) what the focal length of L2 is. That is where you need to think a little about the apparently "not so useful" hint about wearing eyeglasses. All of us have a positive lens in our eyes. Let us call it L1. When glasses are worn, one can either use a positive (far sighted) or a negative lens (short sighted) to bring the image focused onto the retina of the eye. What this means, is that the eyeglasses play the role of L2.

Now this should help in solving this problem. As for (ii), the answer is actually independent of the focal length of L2.

Do solve it in BOTH CASES, i.e. have TWO ray diagrams: L2 is positive and L2 is negative.