1. Diffraction
Chapters 31

2. Wave Motion
Waves propagate in all directions without barriers

3. Wave Fronts
Line that represents waves that are all in phase, usually crests

4. Huygens Principle
Every point on a propagating wave front serves as a source of a spherical secondary wavelet
The corresponding spherical wavelets produce further wave fronts
Basis for Diffraction, Reflection, Refraction

5. Huygens Principle

6. Huygens Principle

7. Huygens Principle First proposed explanation that light is a wave
Newton later proposed that light is a particle

8. Diffraction
Bending of waves around an obstacle or the edges of an opening
Example:
You can often hear people in the hallway without seeing them
Shadows

9. Sound Diffraction

10. Diffraction

11. Diffraction

12. Diffraction
Causes interference patterns a certain distance away from the source
Bright and dark spots for light
Loud and dead spots for sound
Amount of diffraction is a measure of distance between consecutive bright spots

13. Young’s Double Slit Experiment
Proof that light acts like a wave
Light shining through 2 slit opening
Bright and dark lines on screen

14. Diffraction Equation x = amount of diffraction λ = wavelength
L = distance from opening to screen
d = distance between slits
d<<L

16. Examples
Applet
Laser Pointer

17. Path Difference

18. Path Difference
For Maximum Constructive Interference the path difference is nλ
For Maximum Destructive Interference, the path difference is (n +1/2)λ