Problem 47

  A figurine is placed 15.0 cm in front of a converging lens (f = 40.0 cm). Using a ray diagram drawn to scale, find (a) the image distance and (b) the magnification.

SOLUTION:
(a) Naturally, I can't draw the picture here, but I'll describe what you should do. First, make a ray from the top of the object passing through the center of the lens. Next, make a ray from the top of the object passing through the focus on the other side of the lens; rays passing through the focus are refracted paraxially, so make a paraxial line where this ray crosses the lens (it's actually on the virtual side of the lens). You'll find an upright, virtual image behind the object. If you were to use the lens equation, you'd find that d_i = -24 cm. When you see a negative image distance for lenses, you know it's on the virtual side.

(b) With your ray diagram, you can see that the image is larger than the object. Using the magnification equation (or, as requested, a carefully drawn ray diagram), you'd find that m = 1.6.