Chapter 22, Problem 1CQ

To determine

Why does the arc of a rainbow appear with red on top and violet on the bottom.

Answer to Problem 1CQ

Refraction through larger angles makes violet to appear at the bottom and the refraction through smaller angle makes red to appear on the top of the arc.

Explanation of Solution

The dispersion of light into a spectrum is most clearly visible in a rainbow. The phenomena behind the formation the rainbow is refraction, reflection and total internal reflection.

When a ray of light strikes a ray of light, it is first refracted at the front surface, with the violet light deviating the most and the red light the least. At the back surface, it undergoes reflection and comes to the front surface where the refraction occurs again. As violet refracts through larger angles, it comes at the bottom of the arc.

Conclusion:

Thus, the refraction through larger angles makes violet to appear at the bottom and the refraction through smaller angle makes red to appear on the top of the arc.