Wave InterferenceJ. Tobler

What is a Wave?A disturbance that carries energy through

matter or space.They carry energy without transporting matterWaves can do work!

Most move through a medium (matter wave travels through)Mechanical Waves need a medium to transfer

the energyElectromagnetic waves do not need a medium,

they can travel through empty space

Where do waves come from?Most waves are caused by vibrating

objectsStrings on a guitarEardrum SpringsCharged particles (in light waves)

Exist only as long as it has energy to carry

Wave VocabularyCrest – high point of a waveTrough – low point of a waveRest position – mid point between crest

and troughAmplitude – distance from rest position to

crest or trough, depends on energyNodes – points where wave crosses rest

positionWavelength (λ) – distance between to

common points on a wave (crest to crest), depends on frequency

Anatomy of a Transverse Wave

Wavelength

()

Nodes

FrequencyHow oftenRepresented as fMeasured in Hertz (Hz)High frequency = short wavelength and vice versa

Inversely related to the period (f = 1/T)

f = # waves / total time

PeriodThe time to complete one cycle or

oscillationRepresented as TMeasured in seconds (s) Inversely related to frequency

(T=1/f)With a low frequency, the time between cycles is greater because the waves don’t pass by as often.

T = total time / # waves

Wave SpeedOr wave velocity

How fast the energy moves through the medium

Depends on the frequency and wavelength

Wave speed depends on the mediumV= f λ

λ = wavelength (m)

Which set of waves has the highest frequency?Which set of waves has the shortest period?Which set of waves has the longest wavelength?Which set of waves has the greatest amplitude?

10 seconds

What happens to a wave when it reaches a boundary?

It will either pass through or reflect the energy depending on the density of the mediums.

If the boundary is very dense and rigid then the wave will just reflect reversing its direction.

When Waves CollideWaves interfere with each otherConstructive Interference

Amplitudes are in the same direction, or “in phase”

Waves add together creating a greater amplitude

Interference is temporary

Constructive Interference

When Waves Collide (Part 2)Destructive Interference

Amplitudes are in opposite directions or “out of phase”

Waves cancel each other out resulting in a smaller amplitude or zero amplitude

Also temporary

Destructive Interference

Notice what happens to the blue wave as the others go in and out of phase with each other.

Standing WavesResult of Constructive and Destructive

Interference caused from wave reflection at fixed boundaries

Video LinksConstructive vs Destructive InterferenceStanding Waves ExplainedWave InterferenceStanding Waves and Strobe LightStanding Wave Demonstration with high speed

camera

Parts of a Longitudinal or Compression Wave

Transverse vs. Longitudinal Waves

Properties of Waves SummaryType of Wave Mechanical Electromagnetic

FormLongitudinal Transverse Modeled as transverse

Medium Solids, liquids, gases

Solids and liquids

None required

Travel asCompression and rarefactions in matter

Back-and-forth (or up-and-down) movement of matter

Oscillating electric and magnetic fields

Examples Sound waves, some earthquake waves

Water waves, rope waves, some earthquake waves

Visible light waves, radio waves, x-rays