Chapter 29, Problem 43A

Very short pulses of red light and blue light enter a glass block normal to its surface at the same time. Which pulse exits first?

To determine

To Explain: The pulse which exits the glass first.

Explanation of Solution

Introduction: 

The light interacts with the materials and that interaction depends on the wavelength of the light. Different colours of light travel at different speeds.

Explanation: 

Slower speeds of light in the glass make the light bend more. This phenomenon is called dispersion. The glass has a higher refractive index for the blue light than the red light.

So, the red-light travels with the higher speed as compared to that of blue light. Therefore, the red-light pulse exits first.

Conclusion: 

The red light exits first because it has low energy.