Chapter 18, Problem 85A

To determine

The reason that a prism bends blue light more than it bends red light.

Answer to Problem 85A

It is because the index of refraction of prism is more for the blue light than for the red light.

Explanation of Solution

Introduction:

Snell’s law of refraction,

  $n_1\sin {\theta }_1=n_2\sin {\theta }_2$

Where,

  $\begin{array}{l}{n}_1=\text{ index of refraction of first medium}\\ n_2=\text{ index of refraction of second medium}\\ {\theta }_1=\text{ angle of incidence}\\ {\theta }_2=\text{ angle of refraction}\end{array}$

As can be seen from above formula, if the index of refraction is more in the refracting medium for a light, its angle of refraction will be less. And, since the index of refraction of prism is more for blue light then for red light, the blue light bends more as compared to red light in prism.

Conclusion:

Due to the difference in index of refraction of prism for blue and red light, one light bends more than the other light.