1. APHY202 3/9/2016 1 24.1 Huygens’ Principle and Diffraction   Isaac Newton – light is a stream of particles   Christian Huygens – light is a wave   Each point on the old wave front is a source for the new wave front.

2. APHY202 3/9/2016 2 24.2 Huygens’ Principle and Refraction   The frequency of light does not change as it travels from one medium to the next.

3. APHY202 3/9/2016 3 24.3 Interference   Thomas Young (1801)

4. APHY202 3/9/2016 4 24.3 Interference

5. APHY202 3/9/2016 5 24.3 Interference   Constructive: d sinθ = mλ m = 0,1,2, …   Destructive: d sinθ = (m+½)λ m = 0,1,2, …

6. APHY202 3/9/2016 6 24.3 Interference

7. APHY202 3/9/2016 7 24.4 The Visible Spectrum and Dispersion

8. APHY202 3/9/2016 8 24.4 The Visible Spectrum and Dispersion

9. APHY202 3/9/2016 9 24.4 The Visible Spectrum and Dispersion

10. APHY202 3/9/2016 10 24.4 The Visible Spectrum and Dispersion

11. APHY202 3/9/2016 11 24.4 The Visible Spectrum and Dispersion