WAVES PROPERTIESWAVES PROPERTIES

Chapter 11, Section 3Chapter 11, Section 3

What is a wave?What is a wave?

A wave is a A wave is a disturbancedisturbance that carries that carries energy energy

through through mattermatter or or spacespace..

Most waves travel Most waves travel through a mediumthrough a medium

A medium is A medium is mattermatter which means it which means it is composed of is composed of particlesparticles. .

Examples of mediums are Examples of mediums are waterwater and and airair. It can also be . It can also be solidssolids such as a such as a slinkyslinky or or roperope..

Waves that Waves that requirerequire a medium to a medium to travel are called travel are called mechanicalmechanical waveswaves..

Electromagnetic waves Electromagnetic waves do not require a do not require a medium.medium. can travel through space can travel through space withoutwithout

the presence of the presence of mattermatter. . consist of changing consist of changing electricelectric and and

magneticmagnetic fields. fields.

Types of wavesTypes of waves

A wave that consists of a single A wave that consists of a single traveling pulse is called a pulse traveling pulse is called a pulse wave.wave.

A group of pulse waves form a A group of pulse waves form a periodic wave.periodic wave.

A wave whose source vibrates A wave whose source vibrates with a simple harmonic motion is with a simple harmonic motion is called a sine wave.called a sine wave.

Longitudinal WavesLongitudinal Waves

Waves that cause particles in a Waves that cause particles in a medium to vibrate medium to vibrate parallelparallel to the to the direction of wave motion.direction of wave motion.

Examples: Sound wavesExamples: Sound waves http://www.kettering.edu/~drussell/D

emos/waves/wavemotion.html

Transverse WavesTransverse Waves

Waves in which the motion of Waves in which the motion of the particles is the particles is perpendicularperpendicular to the motion of the wave as to the motion of the wave as a whole.a whole.

Examples: Light wavesExamples: Light waves http://www.kettering.edu/~drusse

ll/Demos/waves/wavemotion.html

Wave PropertiesWave Properties

Crest – the Crest – the highesthighest pointpoint of a of a transverse wave.transverse wave.

Trough – the Trough – the lowestlowest pointpoint of a of a transverse wave.transverse wave.

Amplitude – the Amplitude – the greatestgreatest distancedistance that that particles in a medium move from their particles in a medium move from their normalnormal positionposition when a wave passes. when a wave passes.

Wavelength – the Wavelength – the distancedistance between between any two any two successivesuccessive identicalidentical parts of a parts of a wave.wave.

Wave Properties Wave Properties DiagramDiagram

WavelengthWavelength

crestcrest amplitudeamplitude

troughtrough

Period & FrequencyPeriod & Frequency

Period – time required for Period – time required for oneone fullfull wavelengthwavelength to pass a certain point. to pass a certain point. Period is measured in Period is measured in secondsseconds (s).(s).

Frequency – the Frequency – the numbernumber of of vibrationsvibrations that occur in that occur in oneone secondsecond. Frequency is measured in . Frequency is measured in HertzHertz (Hz).(Hz).

Equation for Period & Equation for Period & FrequencyFrequency

f = frequency (Hz)f = frequency (Hz)

T = period (s)T = period (s)

f = 1 / Tf = 1 / T

T = 1 / f T = 1 / f

Practice ProblemPractice Problem

1) 20 waves passed in 10 1) 20 waves passed in 10 seconds. What is the seconds. What is the frequency and period of frequency and period of the wave?the wave?

f = 2 Hzf = 2 Hz

T = 0.5 sT = 0.5 s

2)2) What is the frequency of a What is the frequency of a wave if it takes 0.25 s for wave if it takes 0.25 s for

one wave to pass a one wave to pass a certain point?certain point?

f = 4 Hzf = 4 Hz

Practice ProblemPractice Problem

3) A wave has a frequency 3) A wave has a frequency of 260 Hz. How long does it of 260 Hz. How long does it take for one of these waves take for one of these waves to pass a specific point in a to pass a specific point in a

medium?medium?

T =.0038 sT =.0038 s

Practice ProblemPractice Problem

4) A boy is floating in the ocean 4) A boy is floating in the ocean near the beach. In 25 s, 5 big near the beach. In 25 s, 5 big waves have passed over the waves have passed over the boy. What is the frequency boy. What is the frequency and period of these waves?and period of these waves?

f = 0.2 Hzf = 0.2 Hz

T = 5 sT = 5 s

Practice ProblemPractice Problem

Relating frequency to Relating frequency to wavelengthwavelength The longer the wavelength, the The longer the wavelength, the

lowerlower the frequency. the frequency.

The shorter the wavelength, the The shorter the wavelength, the higherhigher the frequency. the frequency.

Relating Frequency & Relating Frequency & PeriodPeriod

The higher the frequency, The higher the frequency, the the shortershorter the period. the period.

The lower the frequency, The lower the frequency, the the longerlonger the period. the period.

Amplitude Amplitude doesdoes notnot affect the affect the wavelengthwavelength or or frequencyfrequency

HighHigh amplitude amplitude

LowLow amplitude amplitude

Pitch & FrequencyPitch & Frequency

The higher the frequency, the The higher the frequency, the higher the pitch.higher the pitch.

The lower the frequency, the The lower the frequency, the lower the pitch.lower the pitch.

Wave SpeedWave Speed

How fast a wave travels.How fast a wave travels.

Speed depends on the Speed depends on the medium.medium. Sound travels through the air at Sound travels through the air at

an average speed of 340 m/s. In an average speed of 340 m/s. In gases, the molecules are far apart gases, the molecules are far apart and move around randomly. A and move around randomly. A molecule must travel through a molecule must travel through a lot of empty space before it lot of empty space before it bumps into another moleculebumps into another molecule

Speed depends on the Speed depends on the medium.medium. In water, sound travels 3-4 times In water, sound travels 3-4 times

faster than it would in air. In faster than it would in air. In liquids, molecules are much liquids, molecules are much closer together and free to slide closer together and free to slide past one another.past one another.

Speed depends on the Speed depends on the medium.medium. In a rock or metal, sounds travels In a rock or metal, sounds travels

15 – 20 times faster that it would 15 – 20 times faster that it would in air. In a solid, molecules are in air. In a solid, molecules are tightly bound to each other. When tightly bound to each other. When one molecules starts to vibrate, one molecules starts to vibrate, all the others start to vibrate all the others start to vibrate almost immediately.almost immediately.

Light has a finite Light has a finite speed.speed. Light travels much faster than Light travels much faster than

sound which is 3 x 10sound which is 3 x 1088 m/s m/s (186,000 miles per second).(186,000 miles per second).

Light travels slower when it has to Light travels slower when it has to go through a medium such as air go through a medium such as air or water.or water.

Doppler EffectDoppler Effect

An observed change in the An observed change in the frequency of a wave when the frequency of a wave when the source or observer is moving.source or observer is moving.

Doppler Effect Doppler Effect ExplanationExplanation When a moving sound source When a moving sound source

moves away from you, the moves away from you, the wavelength near you gets longer. wavelength near you gets longer. The longer the wavelength, the The longer the wavelength, the lower the frequency which causes lower the frequency which causes you to hear a lower pitch.you to hear a lower pitch.

Doppler Effect Doppler Effect ExplanationExplanation When a moving sound source When a moving sound source

moves towards you, the moves towards you, the wavelength near you gets wavelength near you gets shorter. The shorter the shorter. The shorter the wavelength, the higher the wavelength, the higher the frequency which causes you to frequency which causes you to hear a higher pitch.hear a higher pitch.

http://www.lon-capa.org/~mmp/applist/doppler/d.htm

Calculating the Calculating the Velocity of a WaveVelocity of a Wave v = speed / velocity (m/s)v = speed / velocity (m/s) λλ = wavelength (m) = wavelength (m) Equations:Equations:

v = f v = f λλ v = v = λλ/T/T

Practice ProblemsPractice Problems

1)1) 1.50 m/s1.50 m/s

2)2) 3 x 103 x 1088 m/s m/s

3)3) 5.77 x 105.77 x 101414 Hz Hz

4)4) 1.5 m1.5 m