Chapter 22, Problem 62RPP

Rainbows How is a rainbow formed? Recall that the index of refraction of a medium is slightly different for different colors. When white light from the Sun enters a spherical raindrop, as shown in Figure 22.25, the light is refracted, or bent. After reflecting off the back surface of the drop, the light is refracted again as it leaves the front surface.

Each drop separates the colors of light. An observer on the ground with her back to the Sun sees at most one color of light coming from a particular drop (see Figure 22.26). If the observer sees rod light from a drop (for example, the top drop in Figure 22.26), the violet light for that same drop is deflected above her head. However, if she sees violet light coming from a drop lower in the sky, the red light from that drop is deflected below her eyes onto the ground. She sees red light when her line of view makes an angle of $42°$ with the beam of sunlight and violet light when the angle is $40°$. Other colors of light are seen at intermediate angles.

Why is violet light refracted more than red light?

a. The violet light travels a shorter distance in the drop than the red light.

b. The red light travels more slowly than the violet light.

c. The refractive index of water for violet light is greater than that for red light.

d. All of the above.