Answer
Whether f is positive or negative, the focal length for violet light has a smaller magnitude than for red light, i.e., the focal point is closer to the lens.
Work Step by Step
As seen in Figure 24-14, for glass, the index of refraction for violet light is slightly greater than it is for red light. The violet light bends more (as seen in Figure 24-15), which brings its focal point closer to the lens itself (than red light’s focal point) and yields a focal length of smaller magnitude.
