3.01-3.07 Longitudinal/Transverse Waves + Wave Speed + Frequency

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29 Terms

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Degree (°)
Unit for measuring angles
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Hertz (Hz)
Unit for measuring frequency

1 Hz = 1 complete cycle per second
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Meter (m)
Unit for measuring length
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Meter/second (m/s)
Unit for measuring speed and/or velocity
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Second (s)
Unit for measuring time
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Wave
Vibrations that transfer energy and information without transferring matter
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Oscillation
Vibration; repeated back-and-forth movement between any 2 states and/or positions of an object due to its displacement from its equilibrium
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Transverse wave
Waves that vibrate or oscillate perpendicular to the direction of energy transfer

* Particle oscillations ⟂ to energy transfer’s direction
* Energy transferred in same direction as wave motion
* Energy transferred but particles of the medium are not
* Particles of the medium are not displaced and not transferred (although they move, they are not displaced because the particles move back and forth along the same axis/line so always return to their original position → hence the displacement of 0)
* Waves can move in solids and on the surface of liquids, but cannot move inside liquids or gases
* Some transverse waves (e.g. electromagnetic waves) can move in solids, liquids, gases, and vacuum
Waves that vibrate or oscillate perpendicular to the direction of energy transfer

* Particle oscillations ⟂ to energy transfer’s direction
* Energy transferred in same direction as wave motion
* Energy transferred but particles of the medium are not
* Particles of the medium are not displaced and not transferred (although they move, they are not displaced because the particles move back and forth along the same axis/line so always return to their original position → hence the displacement of 0)
* Waves can move in solids and on the surface of liquids, but cannot move inside liquids or gases
* Some transverse waves (e.g. electromagnetic waves) can move in solids, liquids, gases, and vacuum
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Examples of transverse waves
* Light waves
* Electromagnetic waves (e.g. radio, light, X-rays)
* Ripples on surface water
* Vibrations on guitar string (or vibrations on any string instrument)
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Longitudinal wave
Waves where the points along its length vibrate parallel to the direction of energy transfer

* Particle oscillations are // to energy transfer’s direction
* Energy transferred in same direction as wave motion
* Energy transferred but particles of the medium are not
* Particles of the medium are not displaced and not transferred because the particles move back and forth along the same axis so always return to their original position → hence the displacement of 0)
* Can move in solids, liquids, and gases
* Cannot move in vacuum because there are no particles
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Examples of longitudinal waves
* Sound waves
* Pressure waves caused by repeated movements in a fluid (liquid or gas)
* Shockwaves (e.g. some seismic waves)
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Seismic wave
Waves that travel through or over Earth and which are generated by movement of the Earth’s tectonic plates
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Transverse wave VS longitudinal wave
* Structure
* Transverse → peaks/crests and troughs
* Longitudinal → rarefactions and compressions
* Vibration
* Transverse → ⟂ to energy transfer’s direction
* Longitudinal → // to energy transfer’s direction
* Vacuum
* Transverse → only electromagnetic waves can travel through vacuum
* Longitudinal → cannot travel through vacuum
* Medium
* Transverse → can move in solids and on the surface of liquids, but not inside liquids or gases
* Longitudinal → can move in solids, liquids, and gases
* Density
* Transverse → constant density
* Longitudinal → changing density
* Pressure
* Transverse → constant pressure
* Longitudinal → changing pressure
* Wave speed
* Transverse → dependent on medium
* Longitudinal → dependent on medium
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How are longitudinal waves drawn/represented?
Drawn as a set of vertical lines with rarefactions and compressions. Direction of energy transfer as well as direction of particle motion are also drawn with arrows to show these are parallel to one another
Drawn as a set of vertical lines with rarefactions and compressions. Direction of energy transfer as well as direction of particle motion are also drawn with arrows to show these are parallel to one another
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Crest (a.k.a. peak)
Highest point on a transverse wave
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Trough
Lowest point on a transverse wave
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Equilibrium
a.k.a. “undisturbed position” or “mean position”

Where all forces are balanced and the resultant force is 0

It is the position that the medium the wave is passing through would rest at if no disturbance (i.e. the wave’s energy and forces) were passing through or exerted onto it (e.g. resting position of a string when we are attempting to demonstrate a transverse wave by swinging it vertically up and down, if there were no disturbances moving through it)

Equilibrium is drawn as a horizontal line that is vertically in the middle of the transverse wave
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Amplitude
Distance from the undisturbed position (equilibrium) to the crest/peak or trough of a wave

It is the maximum (if crest/peak) or minimum (if trough) displacement from the undisturbed position (equilibrium); amplitude is a vector so can have a positive (crest - equilibrium) or negative (trough - equilibrium) value

Measured in meters (m)
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Wavelength
Distance between one point on a wave to the same point on the next wave; it is the length of a complete wave cycle

Measured in meters (m)

Usually represented by the Greek letter lambda or λ
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Rarefaction

Region in a longitudinal wave where the particles are furthest apart, usually depicted by drawing the vertical lines farther away from one another

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Compression
Region in a longitudinal wave where the particles are closest together, usually depicted by drawing the vertical lines closer to one another
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Wavefront
Useful diagrams that depict waves from a top view looking downwards (i.e. the lines we see are drawings of the wave’s crests/peaks)

Each vertical line/wavefront represents a crest/peak

Gaps between lines (i.e. gaps between successive crests/peaks) represent wavelength

* short gap → short wavelength
* long gap → long wavelength

Arrow (sometimes called a ray) depicts direction of wave motion
Useful diagrams that depict waves from a top view looking downwards (i.e. the lines we see are drawings of the wave’s crests/peaks)

Each vertical line/wavefront represents a crest/peak 

Gaps between lines (i.e. gaps between successive crests/peaks) represent wavelength

* short gap → short wavelength
* long gap → long wavelength 

Arrow (sometimes called a ray) depicts direction of wave motion
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Frequency
Number of complete waves passing through a point per second

Measured in Hertz (Hz) where 1Hz = 1 complete wave passing through per second
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Period (sometimes also called time period)
Time taken to complete 1 full wave cycle/vibration

Time taken for 1 full wave cycle/vibration to pass through a single point

Measured in seconds (s)
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Wave speed equation
Wave speed (m/s) = Frequency (Hz) \* Wavelength (m)

v = f \* λ
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Relationships (proportionalities) between wave speed, frequency, and wavelength
* frequency ∝ wave speed (for constant wavelength)
* ↑ frequency → ↑ wave speed
* ↓ frequency → ↓ wave speed
* direct proportionality
* wavelength ∝ wave speed (for constant frequency)
* ↑ wavelength → ↑ wave speed
* ↓ wavelength → ↓ wave speed
* direct proportionality
* frequency ∝ 1/wavelength (for constant wave speed)
* ↑ frequency → ↓ wavelength
* ↓ frequency → ↑ wavelength
* inverse proportionality
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Frequency equation
Frequency (Hz) = 1 / Time period (s)

f = 1 / T
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Relationship (proportionality) between frequency and time period
* ↑ time period → ↓ frequency
* ↓ time period → ↑ frequency
* inverse proportionality
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Wave speed in uniform medium
Wave speed stays constant in uniform medium

Even if wavelength changes, if waves are in the same medium, then the wave speed will stay uniform (frequency will decrease instead)