1. The Wave Nature of Light

2. Waves vs Particles

3. Huygens’ Principle
Every point on a wave front can be considered as a source of tiny wavelets that spread out in the forward direction at the speed of the wave itself. The new wave front is the envelope of all wavelets – the tangent to all of them.

5. The bending of waves behind the obstacles into the “shadow region” is known as diffraction.

6. Huygens’ Principle and the Law of Refraction

7. Important: When a light wave travels from one medium to another, its frequency does not change, but its wavelength does.

8. Interference: Young’s Double Slit Experiment

11. Constructive Interference:
Destructive Interference:

12. Line Spacing for Double-Slit Interference

13. Conceptual Example: Changing the Wavelength
What happens to the interference patter if the incident light (500 nm) is replaced by light of wavelength 700 nm?
What happens instead if the slits are moved farther apart?