1. Interference

2. Overlap  Waves from multiple point sources overlap. Crest on crest Trough on trough Crest on trough  Overlapping waves add directly. Principle of superposition

3. Coherence  When wavelengths match crests and troughs can line up. Single frequency Single color  This is called coherent radiation. Example: laser light  Phase matters with coherent light.

4. Constructive Interference  When coherent waves have the same phase the result is constructive interference. Amplitudes addAmplitudes add Intensity follows the square of the amplitudeIntensity follows the square of the amplitude

5. Destructive Interference  When coherent waves have the opposite phase the result is destructive interference. Cancellation of amplitudeCancellation of amplitude Decreased intensityDecreased intensity

6. Path Length  Different path lengths correspond to different phase.  Whole wavelengths give constructive interference.  Half wavelengths give destructive interference.

7. Power Shift  Spacing in coherent electromagnetic waves results in power fluctuations.  Example: microwaves reflecting off mirrors. Transmitter T, monochromatic waves Receiver R, power depend on separation

8. Intensity Pattern  CDs and DVDs are read by intensity difference due to phase shifts. next