1. Properties of WavesProperties of Waves
May 4, 2014May 4, 2014

2. ObjectivesObjectives
1.1. Recognize the different types of wavesRecognize the different types of waves
2.2. Sketch and identify the different parts ofSketch and identify the different parts of
a transverse wavea transverse wave
3.3. Define and calculate the properties ofDefine and calculate the properties of
waveswaves

3. WavesWaves
 Not just the ones you surf on!!!!Not just the ones you surf on!!!!
 A vibration that moves through space andA vibration that moves through space and
timetime

Light and soundLight and sound

4. Types of WavesTypes of Waves
1.1. Transverse wavesTransverse waves
2.2. Longitudinal or Compressional waves -Longitudinal or Compressional waves -
soundsound
3.3. Electromagnetic waves – lightElectromagnetic waves – light

5. Common pointsCommon points
 Crests and TroughsCrests and Troughs
 Midpoints – horizontal line between theMidpoints – horizontal line between the
crests and troughscrests and troughs

6.  Amplitude – distance from the midpoint toAmplitude – distance from the midpoint to
the crest or troughthe crest or trough
 Wavelength – distance from one crest toWavelength – distance from one crest to
the next (any consecutive point)the next (any consecutive point)

7.  Wave train – two or more waves in a row

8. 0 x

9.  Frequency – the number of vibrations theFrequency – the number of vibrations the
object makes during a certain time intervalobject makes during a certain time interval
(s)(s)

F = Cycles/SecondsF = Cycles/Seconds

Measured in Hertz (Hz)Measured in Hertz (Hz)

10.  Period – time it takes for a completePeriod – time it takes for a complete
vibrationvibration

Period = Seconds/CyclesPeriod = Seconds/Cycles

Period and Frequency are relatedPeriod and Frequency are related
Frequency = 1/Period Period = 1/FrequencyFrequency = 1/Period Period = 1/Frequency

11. ExamplesExamples
1.1. An electric toothbrush completes 90An electric toothbrush completes 90
cycles every second. What is it’scycles every second. What is it’s
frequency? What is its period?frequency? What is its period?
2.2. Gusts of wind cause the Sears buildingGusts of wind cause the Sears building
in Chicago to sway back and forth,in Chicago to sway back and forth,
completing a cycle every ten seconds.completing a cycle every ten seconds.
What is its frequency? What is itsWhat is its frequency? What is its
period?period?

12. Problem
 A weight suspended from a spring bobs
up and down over a distance of 20 cm
twice each second. What is its frequency?
Its period? Its amplitude?

13. Waves transport energyWaves transport energy
 How much energy depends on waveHow much energy depends on wave
speedspeed
 Wave speed = frequency x wavelengthWave speed = frequency x wavelength

14. ExamplesExamples
1.1. If a train of freight cars, each 10m long,If a train of freight cars, each 10m long,
rolls by you at the rate of three cars eachrolls by you at the rate of three cars each
second, what is the speed of the train?second, what is the speed of the train?
2.2. If a water wave vibrates up and downIf a water wave vibrates up and down
three times each second and thethree times each second and the
distance between the wave crests is 2m,distance between the wave crests is 2m,
what is the wave’s frequency? Itswhat is the wave’s frequency? Its
wavelength? Its wave speed?wavelength? Its wave speed?

15. Problem
 A skipper of a boat notices wave crests
passing his anchor chain every 5s. He
estimates the distance between wave
crests to be 15 m. He also correctly
estimates the speed of the waves. What
is this speed?

16. Frequency and Wave Speed
May 13, 2011