1. Interference

2. Superposition • Two particles cannot occupy the same space at the same time, two waves can • When two waves interact, one is super imposed on the other • The resultant wave is a combination of both waves

3. Constructive Interference • Constructive interference occurs when similar parts of both waves occupy the same point in space • Transverse Waves • Crest meets crest • Trough meets trough • Longitudinal Waves • Compression meets compression • Expansion meets expansion • Resultant wave with greater amplitude

4. Destructive Interference • Destructive interference occurs when different parts of both waves occupy the same point in space • Transverse Waves • Crest meets trough • Longitudinal Waves • Compression meets expansion • Resultant wave with much smaller (or zero) amplitude

6. Phase Difference • Phase difference refers to the alignment of two waves • A phase difference of 0° or 360° (0, 2π) means the waves are in-phase • Constructive interference • A phase difference of 180° (π) means the waves are out of phase • Destructive interference

7. Noise Cancelling Headphones • Uses destructive interference to eliminate background noise • A microphone detects incoming sounds • Speaker produces opposite signal, destructively interferes with ambient noise

8. Multi-point interference • Waves created by two or more different sources interfere with each other

9. Reflectance • When a wave encounter a boundary some of the wave is reflected back • The reflectance depends on the material of the boundary • The reflected waves interfere with the incoming waves

10. Auditoriums vs. Gymnasium