Wave Interference Physics Ch 12. Sec. 4

- When two waves come together they can occupy the same space  Superposition – multiple waves occupying the same space - Mechanical and electromagnetic electromagnetic waves can do this waves can do this

Wave Interactions Interferance – combination of 2 or more waves combination of 2 or more waves  usually produces one wave  usually produces one wave (bigger if in phase) (smaller if out of phase)

Types of Interference 1. Constructive Interference – individual displacements on the same side of equilibrium add together to form a resultant wave (in phase) - If two pulses move toward each other and are on the same side of equilibrium their amplitudes add together to form a larger wave

Wave Interactions Constructive interference – when waves combine to create a bigger wave  sum of the amplitudes of the waves

- They move through and past each other - Superposition principle – method of summing the waves to get a resultant wave

Wave Interactions 2. Destructive interference – when waves combine to form a smaller or no wave  some may completely cancel out  difference between the amplitudes of the waves

2. Destructive interference – individual displacements on opposite sides of equilibrium are added together to form a resultant wave (out of phase)

Reflection - When a wave strikes a boundary it bounces (reflects) off of that boundary

1. Free boundary – pulse is reflected identical to the pulse  The rope / spring / medium is free to medium is free to move up and move up and down at the down at the boundary boundary

2. Fixed boundary – pulse is reflected but is inverted  The rope / spring / medium is tightly medium is tightly secured at the secured at the boundary and is boundary and is not free to move not free to move up or down up or down

 Standing waves  - Wave pattern that appears to stand still from waves traveling in opposite directions   Waves at same frequency   Creates spots of zero displacement

- Node – point on a wave that stands still due to total destructive interference always occurring - Antinode – point on a standing wave halfway between two nodes (point of largest displacement) *Only certain frequencies produce standing waves

Wave Behaviors A. Refraction - bending of waves as they pass from one medium to another

Wave Behaviors B. Diffraction – bending of waves around an edge

Wave Interactions - Wave speed depends on the medium ex. Sound  moves fastest through solids  moves moderately fast through liquids  moves slowest through air/gases (340 m/s) - due to movement of molecules in the medium

Wave Interactions Light travels at a constant speed 3x 10 8 m/s = 300,000,000 m/s (186,000 miles/sec.) - symbolized as “c”