Physics 20: Waves Cheat Sheet

Bold formulae are not given on the Physics 20 formula sheet

Along the pulse, energy is stored in both elastic potential and kinetic energy
- At max displa­cement, PE is at max and KE is zero
- At equili­brium, KE is at max

The greater the amplitude, the greater the energy of the wave

Reflec­tion: When a wave reflects, it exhibits a phase change (crest -> trough or vice-v­ersa)
Refrac­tion:
Diffra­ction:
Interf­erence:

Standing Waves: when 2 wave trains with the same amplitude and wavelength move through each other, the resulting interf­ering pattern results in a standing wave, it appears to be standing still in a constance position
- The freque­ncies at which standing waves exist are the natural or fundam­ental resonant frequency

Nodes: points of complete destru­ctive interf­erence
Antinodes: points of complete constr­uctive interf­erence

Reflec­tion: straight waves "­bou­nce­" off a surface such that the outgoing angle (angle of reflec­tion) or reflection wave equal the incoming angle (angle of incidence) or incident wave

Angles are measure from the normal line (line perpen­dicular to the surface)

Wave Train: a series of waves linked together in phase (moving with identical motion)

Wave fronts are reflected by a barrier

When a wave passes from one medium to another through a boundary, the waves bends and changes direction (and speed) at the interface

If the medium on the other side is '­thi­cke­r' (n), then the wave will slow down and bend towards the normal line

Diffra­ction: waves bend around a corner or opening

The amount of diffra­ction depends on the wavelength and the size of the opening

Waves lose amplitude, not speed or frequency

Constr­uctive: "in phase" waves produce larger amplitudes
Destru­ctive: "out of phase" waves amplitudes cancel

Principle of Superp­osi­tion: the two waves "­sup­eri­mpo­se" and "­int­erf­ere­" with each other, creating a temporary waveform that is the sum of the two waves

Fo = observers frequency
Fs = emitted frequency
V = speed of sound
Vs = speed of object emitting sound

Subtract when the source is moving towards the observer
Add when the source is moving away from the observer

Stringed Resonator: a resonating instrument that is fixed at both ends

Closed­-Pipe Resonator: tube is closed at one end and open at another

In a closed­-tube, node at closed end and either node or antinode at open end.
IF antinode occurs at the open end, resonance occurs and the sound is amplified (louder).
IF a node occurs at the open end, resonance does not occur and almost no sound (hence only odd harmonics)

Open-Pipe Resonator: both ends of the tube are open