1 24 Overview wave effects: interference, diffraction polarization, scattering Homework: 1, 12, 43, 57, 67.

2 waves pass through another wave undisturbed diffract video demo simulationvideo demosimulation Reflect wave tank demowave tank demo

3 Interference amplitude change due to adding waves correlation (Coherence) - required for strong interference effects misalignment of waves (phase) is zero for constructive (bright) 180 deg: destructive (dark) Wave tank demo

4 double-slit experiment coherent light Interference pattern path difference

5 central max m = 1 bright fringe m = 2 bright fringe m = 1 dark fringe m = 2 dark fringe m = 3 dark fringe L naming convention

6 Double-Slit Phase Difference Bright: (dsin  ) = 0, 1, 2, … wavelengths Dark: (dsin  )= ½, 1½, 2½, … wavelengths

7 Single Slit Pattern

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9 Polarizing Filters Polarizing material allows the passage of only one direction of E Malus ’ Law:

10 Two Filters (incident light unpolarized) 1 st reduces intensity by 1/2. 2 nd reduces according to Malus’ Law

11 Polarization by Scattering and Reflection Light scattered at 90 degrees is 100% polarized.

12 Summary all waves diffract & interfere coherence required for strong effect path difference determines interference for double-slits and thin-films light polarization & polarizing filters

13 thin-film interference causes certain colors to become more or less intense. Ex. oil on water, soap bubble, coatings 1+2 constructive or destructive

14 Reflection phase off higher index: ½ wavelength phase change (Ex. ray 1 in diagram) off lower index: 0 (Ex. ray 2 in diagram)

15 Thin Film Problem Solving * 0: no reflection phase changes (or two) * ½: one reflection phase change

16 Ex. t = 100nm. Light wavelength = 400nm in water. Ray 1 has reflection phase change, Ray 2 does not. (= ½) Bright

17 diffraction grating N = #lines/cm, Spacing: d = 1/N Video demo

18 a = Slit-Width (a ≠ d) Single Slit Diffraction

19 waves pass through another wave undisturbed diffract video demovideo demo Refract and reflect