Unit 9 – Lecture 1

Wavesrhythmic disturbances which transmit energy through a medium [substance – solid, liquid,

or gas]

ex: light & sound[note: sound and other types of waves can carry information in the form of energy]

WavesCord Demo – does the cord itself move from

place to place? is it traveling with the wave?

Waves move through the medium – they do not move the medium itself.like the wave at a sporting event

Types of WavesMechanical waves – need to travel through

mattertransverse wavescompressional [aka longitudinal]

Water waves move in a combination of these movements

Transverse WavesTransverse waves

matter in medium moves back and forth at right angles to the wave’s energy

Electromagnetic rays travel in transverse waves

if wave is traveling L or R, the movement of the medium is up and down.

if wave is traveling up or down, the movement of the medium is L & R

Transverse WavesParts of a Transverse Wave

draw this wave on your paperin the space provided.

Transverse WavesParts of a Transverse Wave

crestthe highest point of the wave – highest Ethere can be many crests

Transverse WavesParts of a Transverse Wave

troughthe lowest point of the wave – lowest Ethere can be many troughs

Transverse WavesParts of a Transverse Wave

resting positiondoes not have to be at zero!

Transverse WavesParts of a Transverse Wave

amplitudethe furthest distance from the resting

positionfrom resting position to either crest or

trough

Transverse WavesParts of a Transverse Wave

wavelengthdistance of one wavedistance between two equal points on a

wave

Transverse Waves

Longitudinal Waves Longitudinal Wave [aka Compressional

Wave]matter in the medium moves back and

forth along the same direction of the wavesound and seismic waves

imagine a coil: a slinky or springcompress coils then

release, wave moves coils in a compression to other side

Longitudinal WavesParts of a Longitudinal Wave

Draw a coil on your sheet like the one below, with areas of densely bound coils, and areas of lesser bound coils

Longitudinal WavesParts of a Longitudinal Wave

rarefactiona non-compressed area of this type of

wavepoint of lowest energy

Longitudinal WavesParts of a Longitudinal Wave

compressiona compressed area of this type of wavepoint of highest energy

Longitudinal WavesParts of a Longitudinal Wave

wavelengthdistance of one wavedistance between two equal points on a

wave

Longitudinal Waves

Transverse vs Compressional Waves

Practice What is a wave?What is the name for the material through

which a wave travels?In which kind of wave do the particles of the

medium vibrate in the same direction as the wave?

What is transmitted by a wave?In which kind of wave do the particles of the

medium vibrate at right angles to the wave?How is a crest similar to a compression / a

trough similar to a rarefaction?

Wave MeasurementsFrequency – number of waves that pass a

certain point per unit of time. [waves per time]measured in Hertz [Hz] for waves per

second

as waves travel faster [higher frequency], the wavelength decreaseswhat type of relationship is this?1 Hz = 1 wave per second

Wave MeasurementsPeriod = time it takes to complete one cycle

[time per wave]T = t / # of wavesOR

this is the inverse of frequencyT = 1/ f

PracticeThe period of a wave is 3 seconds.

What is its frequency?

Wave MeasurementsWave Speed can depend on the medium

sound travels best through solids [particles close together] but radio waves and others can’t travel through them

Wave MeasurementsCalculating Wave Speed

recall: speed = distance / timerecall: frequency = waves/time

wave speed = wavelength * frequencyv = λ * f

does this make sense? let’s seewave speed (m/s) = wavelength (m) * waves (#)

time (s)

Electromagnetic WavesElectromagnetic Waves – do not need matter

to transfer energy wave transferred by vibration of

magnetic & electric fieldsEMS = range of electromagnetic radiationEMS contains Visible Light in roughly the

center of spectrum R O Y G B I V

Electromagnetic Wavesall EM waves travel at the speed of light

roughly 3 x 108 m/s or 186,282.6 miles per second

variable for speed of light = Cthis is currently the fastest speed in the

universe

Electromagnetic Spectrum

Electromagnetic SpectrumHow to remember?

Electromagnetic SpectrumHelpful Prefixes:

mega = M = 1 x 106

nano = n = 1 x 10-9