Waves and Sound Flashcards
Wave
A disturbance in some medium in which the parts of the medium are displaced and the displacement changes with time due to interactions between the parts
Travelling wave
A disturbance that travels in some direction with a particular speed
Transverse wave
A wave in which the displacement is perpendicular to the direction of travel of the wave
- wave on a string
- wave on water
Longitudinal wave
A wave in which the displacement is in the same direction that the sound wave is travelling in
- slinky waves
- sound waves
Snapshot graph
Shows the displacement as a function of the position along the wave at a specific time
History graph
Shows the displacement at one location as a function of time
Determines the sound that we hear (the sound wave at the location of our ear)
Sinusoidal waves
Waves with a sinusoidal shape (history graph)
Caused by simple harmonic oscillations
Wavelength of a sinusoidal wave
The distance in space between neighbouring peaks
Frequency/period of a sinusoidal wave
The frequency/period of oscillation for any point on the wave
Wave speed
The rate at which the features of a wave travel in the direction that the wave is moving
How are wavelength, frequency/period, and wave speed related?
Pressure
In a gas, the force that it exerts per unit of area
Measured in Pascals
1 Pascal = 1 Newton per square metre
Standard atmospheric pressure
100,000Pa / 100kPa
Force of a gas on a surface
F = P A
Force, pressure, area
Density of molecules & pressure
Molecules per unit volume
Pressure is proportional to density of molecules (for a fixed temperature)
How does a microphone work?
A membrane vibrates in response to the changes in pressure caused by a sound wave
The microphone converts the displacement of the membrane as a function of time to a recordable electrical signal
How does a speaker work?
A speaker converts electrical signals into the motion of an object that displaces the air molecules to create a sound wave
The principle of superposition
Multiple sound waves can travel in the same medium without disturbing each other
The net displacement due to a combination of waves is the sum of the displacements that each wave would have individually
Fourier’s theorem
Any periodic time graph can be decomposed as a sum of sinusoidal time graphs with frequencies f, 2f, 3f, 4f, etc.
Any musical tone (f) is equivalent to a combination of pure tones with frequencies f, 2f, 3f, 4f, etc.
f: the fundamental
2f: the second harmonic
3f: the third harmonic
What is the difference between musical and non-musical sounds?
Non-musical sounds can also be understood as a combination of pure tones, but they generally involve a wide range of frequencies
Spectrum
The information about the pure-tone frequencies present in a sound and the amount of each
Spectrum graph
Shows the amplitude of each frequency of pure tone present in a sound
Standing wave
A combination of a travelling sinusoidal wave moving to the left and a travelling sinusoidal wave with the same wavelength moving to the right, superimposed
Has a sinusoidal shape which simply oscillates up and down
Nodes and antinodes remain in the same place
Nodes
Constant places in a standing wave with zero displacement (while rest of wave oscillates up and down)
On a stretched string fixed at both ends, a node must be at both ends
- allowed wavelengths are 2L, L, 2L/3, L/2, etc. (2L divided by any whole number)
In a cylindrical tube, closed ends have a node, and open ends have an antinode