J. Tobler

What is a Wave? A disturbance that carries energy through matter or space. They carry energy without transporting matter Waves can do work! Most move through a medium (matter wave travels through) Mechanical Waves need a medium to transfer the energy Electromagnetic waves do not need a medium, they can travel through empty space

Where do waves come from? Most waves are caused by vibrating objects Strings on a guitar Eardrum Springs Charged particles (in light waves) Exist only as long as it has energy to carry

Wave Vocabulary Crest – high point of a wave Trough – low point of a wave Rest position – mid point between crest and trough Amplitude – distance from rest position to crest or trough, depends on energy Nodes – points where wave crosses rest position Wavelength (λ) – distance between to common points on a wave (crest to crest), depends on frequency

Anatomy of a Transverse Wave Wavelength ( ) Nodes

Frequency How often Represented as f Measured in Hertz (Hz) High frequency = short wavelength and vice versa Inversely related to the period (f = 1/T) f = # waves / total time

Period The time to complete one cycle or oscillation Represented as T Measured 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 Speed Or wave velocity How fast the energy moves through the medium Depends on the frequency and wavelength Wave speed depends on the medium V= 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 Collide Waves interfere with each other Constructive 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 Waves Result of Constructive and Destructive Interference caused from wave reflection at fixed boundaries Video Links Constructive vs Destructive Interference Standing Waves Explained Wave Interference Standing Waves and Strobe Light Standing Wave Demonstration with high speed camera Standing Wave Demonstration

Parts of a Longitudinal or Compression Wave

Transverse vs. Longitudinal Waves

Properties of Waves Summary Type of Wave MechanicalElectromagnetic Form LongitudinalTransverseModeled as transverse Medium Solids, liquids, gases Solids and liquids None required Travel as Compression 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