Answer
a. Violet
b. Red
Work Step by Step
a. For the diffraction grating, violet light will be at the top of the rainbow, closer to the centerline and the original direction of the light beam. This is shown in Figure 24-26. The maxima are found at angles determined by equation 24-4. Violet light’s shorter wavelength means that their fringes appear at a smaller angle away from the centerline.
b. If a prism is used, red light will be at the top of the rainbow, closer to the centerline and the original direction of the light beam. This is shown in Figure 24-15. The index of refraction for violet light in glass is slightly greater than it is for red light. Red light will bend less and will appear closer to the centerline, which is the direction of the original, horizontal incident beam.