# Waves 1 Chapter 25.

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Waves 1 Chapter 25

Vocabulary Wave Pulse Medium
Vibratory disturbance that propagates (moves) through a medium Pulse Single disturbance Medium Material through which a wave propagates

Waves Waves transfer energy from one place to another, not mass

Wave Types Two main types Transverse Longitudinal
Motion of the disturbance is perpendicular to the direction of the wave propagation Longitudinal Motion of the disturbance is parallel to the direction of the wave propagation

Transverse Waves Motion of the disturbance is perpendicular to the direction of the wave propagation Example: Light TRANSVERSE WAVES

Longitudinal Waves Motion of the disturbance is parallel to the direction of the wave propagation Example: Sound LONGITUDINAL WAVES

Surface Waves Combination of transverse and longitudinal waves
Example: Water

Water Waves (surface)

Wave Characteristics Amplitude, A (m) Wavelength, λ (m) Period, T (s)
Displacement away from equilibrium point Wavelength, λ (m) Length of 1 wave cycle Period, T (s) Amount of time for 1 wave cycle

Wave Characteristics (cont)
Crest λ (m) A T (s) Trough

Wave Characteristics (cont)
Frequency, f (Hz or s-1) Number of cycles per second Inverse of period Speed, v (m/s) How fast wave is traveling Related to frequency (period) and wavelength

Equations f = frequency (Hz) T = period (s) v = speed (m/s)
λ = wavelength (m)

Light Light is also called electromagnetic radiation
Light is a combination of fluctuating electric fields and magnetic fields that are perpendicular to each other

Electromagnetic Spectrum

Electromagnetic Spectrum
R Radiowave M Microwave I Infrared V Visible U Ultraviolet X X-Rays G Gamma C Cosmic Wavelength Decreases Frequency Increases Energy Increases

Light (cont) Transverse Wave Travels through vacuum
Color is based on frequency Green Light = 5.6 x 1014 Hz Speed of light in a vacuum (air also) c = 3 x 108 m/s

Sound Longitudinal Wave Needs a material (medium) to move
Pitch is based on frequency Concert A = 440 Hz Speed of Sound in air is dependent on Temp v = 331 m/s at STP

Wave Speed Waves must follow the kinematic equation
The speed of waves depends upon the material that the wave travels through

Wave Speed Sound can not travel in a vacuum, light can
Light travels fastest in a vacuum, slower in all other materials Sound travels faster in more dense materials

Phase Difference Two points are considered “in phase” when they are at the same point in a wave cycle The amount of “in or out of phase” is measured in degrees

Phase Difference Examples
What point is in phase with A? B and D are how far out of phase? Name two other points in phase with each other.

Wave Motion Waves propagate in all directions without barriers

Wave Fronts Line that represents waves that are all in phase, usually crests

Principle of Superposition
When two waves meet, they combine together briefly, then go their separate ways Crest + crest = bigger amplitude Trough + trough = bigger amplitude Crest + trough = lower amplitude

Interference Constructive Interference Destructive Interference
When 2 waves interfere with resultant wave having larger amplitude Destructive Interference When 2 waves interfere with resultant wave having smaller amplitude

Simulation Examples

Interference Example Two point sources (green dots)
What do the red dots represent? What do the blue dots represent?

Sound Beats Interference produced when two sounds interact
Frequency of beats is equal to difference of frequencies of two sounds Concept used to tune pianos Demo

Standing Waves Occurs when two waves traveling in opposite directions in the same medium, with the same amplitude and same frequency Resultant wave appears to be standing still Demo

Nodes and Antinodes Nodes Antinodes
Points of maximum destructive interference Antinodes Points of maximum constructive interference

Nodes and Antinodes

Nodes and Antinodes

Doppler Effect Change in frequency due to moving wave source or observer Example

Doppler Effect When distance between source and observer is decreasing, frequency increases Blue Shift When distance between source and observer is increasing, frequency decreases Red Shift

Sonic Boom When moving object exceed the speed of sound, air builds up into a shock wave

Sonic Boom

Video YouTube Video How does this work?

Resonance Natural Frequency Resonance
Particular frequency that every elastic body will vibrate at if disturbed Resonance Vibration of a body at its natural frequency because of the action of a vibrating source of the same frequency

Real Life Microwaves produce waves that have the same frequency as the vibrational frequency of water molecules UV rays have the same frequency as certain chemicals in human skin, causing sun burns Google – Tacoma Narrows Bridge

Harmonics Fundamental Frequency(1st Harmonic)
Lowest frequency possible 2nd Harmonic 2x frequency of 1st Harmonic (Octave higher)

Closed Pipe Harmonics (Lab)
1st Harmonic L = 1/4  = 4L 3rd Harmonic L = ¾   = 4/3L 5th Harmonic L = 1 1/4   = 4/5L

Open Pipe Harmonics 1st Harmonic L = ½ =2L 2nd Harmonic L = 
3rd Harmonic L = 1 ½  =2/3L