WAVE BasicsWAVE BasicsChapters 15Chapters 15

What are Waves?What are Waves?

• A A wavewave is a disturbance that is a disturbance that transmits energy through transmits energy through matter or space.matter or space.

Types of WavesTypes of Waves• There are two types There are two types

of waves:of waves:– MechanicalMechanical: Require : Require

a a mediummedium (matter (matter through which a through which a wave travels)wave travels)

• Examples Include:Examples Include:– Ocean waves, medium Ocean waves, medium

= water= water– Sound waves, medium Sound waves, medium

= air= air– Seismic Waves Seismic Waves

(Earthquake), medium (Earthquake), medium = earth= earth

Types of WavesTypes of Waves– ElectromagneticElectromagnetic: :

caused by a disturbance caused by a disturbance in electric and magnetic in electric and magnetic fields and do not require fields and do not require a medium.a medium.

• Examples include:Examples include:

Wave MovementWave Movement• A A wave front wave front is the front of a wave that is the front of a wave that

is transferring energy. is transferring energy. – In a single system all of the wave fronts In a single system all of the wave fronts

have the same amount of energy, but as have the same amount of energy, but as the wave front spreads out, so does the the wave front spreads out, so does the energy. energy.

Wave MovementWave Movement• Waves can move in two basic ways:Waves can move in two basic ways:

– Transverse Motion:Transverse Motion: particles of the medium vibrate particles of the medium vibrate perpendicularly to the direction the wave travels. perpendicularly to the direction the wave travels.

• Example: light waveExample: light wave– LongitudinalLongitudinal (Compressional) Motion:(Compressional) Motion: particles of the particles of the

medium vibrate parallel to the direction the wave medium vibrate parallel to the direction the wave travels.travels.

• Example: sound waveExample: sound wave

Parts of a WaveParts of a Wave• You will be responsible for identifying parts of You will be responsible for identifying parts of

a wave on both a transverse and longitudinal a wave on both a transverse and longitudinal wave. Complete the descriptions and label wave. Complete the descriptions and label the following on your note outline:the following on your note outline:

Parts of a WaveParts of a Wave

• Transverse Wave: The Transverse Wave: The top of the wave is called top of the wave is called a a crest (peak)crest (peak); the ; the bottom of the wave is bottom of the wave is called the called the troughtrough..

• Longitudinal Wave: The Longitudinal Wave: The point of maximum point of maximum compression is called a compression is called a compressioncompression; The point ; The point of least amount of of least amount of compression is called a compression is called a rarefactionrarefaction..

Parts of a WaveParts of a Wave• Wavelength (Wavelength (λλ)) is the total is the total

length of 1 wave.length of 1 wave.– In transverse waves it’s In transverse waves it’s

typically measured from crest typically measured from crest to crest or trough to trough.to crest or trough to trough.

– In longitudinal waves it’s In longitudinal waves it’s measured from compression measured from compression to compression or rarefaction to compression or rarefaction to rarefaction.to rarefaction.

– The shorter the wavelength, The shorter the wavelength, the more energy the wave is the more energy the wave is carrying.carrying.

Parts of a WaveParts of a Wave• AmplitudeAmplitude c can be measured on a transverse wave. It an be measured on a transverse wave. It

height from the resting point to the crest or the resting height from the resting point to the crest or the resting point to the trough.point to the trough.– The larger the The larger the amplitudeamplitude, the more energy the wave is , the more energy the wave is

carrying.carrying.

Wave MeasurementsWave Measurements

• A A period (T)period (T) is the is the time it takes for time it takes for one full one full wavelength of wavelength of wave to pass a wave to pass a certain point.certain point.

– A period is a A period is a measurement of measurement of time, so its SI unit time, so its SI unit is seconds (s).is seconds (s).

Wave MeasurementsWave Measurements

• The The frequency (f)frequency (f) of of a wave is the a wave is the number of full number of full wavelengths that wavelengths that pass a given point pass a given point per second.per second.

– The SI unit for The SI unit for measuring frequency measuring frequency is Hertz (Hz). is Hertz (Hz).

Wave MeasurementsWave Measurements

• The The frequency (frequency (ff)) of a of a wave is the number of wave is the number of full wavelengths that full wavelengths that pass a given point per pass a given point per second.second.

– The SI unit for The SI unit for measuring frequency is measuring frequency is Hertz (Hz).Hertz (Hz).

– Frequency is the inverse Frequency is the inverse of periodof period

• ff = 1 / T = 1 / T

Wave MeasurementsWave Measurements• Wave speed (v) Wave speed (v) is the speed at which a wave passes is the speed at which a wave passes

through a medium and is measured using the through a medium and is measured using the following equation:following equation:

wave speed (m/s) = frequency (Hz) x wavelength (m)wave speed (m/s) = frequency (Hz) x wavelength (m)

v = f x λv = f x λ

Wave MeasurementsWave Measurements

• A wave along a guitar string has a A wave along a guitar string has a frequency of 440 Hz and a wavelength of frequency of 440 Hz and a wavelength of 1.5 m. What is the speed of the wave?1.5 m. What is the speed of the wave?

v =

? m/s

f =

440 Hz

λ =

1.5 m

v = 440 Hz x 1.5 m

v = 660 m/s

v = f * λ

v

f * λ

Wave MeasurementsWave Measurements

• The speed of sound in air is about 340 The speed of sound in air is about 340 m/s. What is the wavelength of sound m/s. What is the wavelength of sound waves produced by guitar strings vibrating waves produced by guitar strings vibrating at a frequency of 440 Hz?at a frequency of 440 Hz?v =

340 m/s

f =

440 Hz

λ =

? m

λ = 340 m/s / 440 Hz

λ = 0.77 m

λ = v / f

v

f * λ

Wave MeasurementsWave Measurements

• The speed of light is 3 x 10The speed of light is 3 x 1088 m/s. What is m/s. What is the frequency of microwaves with a the frequency of microwaves with a wavelength of 0.01 m?wavelength of 0.01 m?v =

3 x 108 m/s

300,000,000 m/s

f =

? Hz

λ =

0.01 m

f = 300,000,000 m/s / 0.01 mf = 30,000,000,000 Hz

f = v / λ

v

f * λ

Wave BehaviorWave Behavior

• A A reflectionreflection is the bouncing back of is the bouncing back of a wave as it meets a surface or a a wave as it meets a surface or a boundary.boundary.

Wave BehaviorWave Behavior• How a wave reflects depends upon How a wave reflects depends upon

the surface that it bounces off of.the surface that it bounces off of.– Example: When sending pulses down Example: When sending pulses down

a rope with a free end, the wave a rope with a free end, the wave comes back normal.comes back normal.

– Example: When sending pulses down Example: When sending pulses down a rope with a fixed end, the wave a rope with a fixed end, the wave comes back inverted.comes back inverted.

Wave BehaviorWave Behavior• DiffractionDiffraction is the is the

bending of a wave bending of a wave as it passes an edge as it passes an edge or an opening.or an opening.

Wave BehaviorWave Behavior• RefractionRefraction is the is the

bending of waves bending of waves as they pass from as they pass from one medium to one medium to another.another.

Wave BehaviorWave Behavior• InterferenceInterference occurs occurs

when the combination when the combination of two or more waves of two or more waves exist in the same exist in the same place at the same place at the same time.time.

– Constructive Constructive interference interference = bigger = bigger wave.wave.

– Destructive interference Destructive interference = smaller wave.= smaller wave.

Wave BehaviorWave Behavior• Standing waves Standing waves are are

caused by two caused by two identical waves going identical waves going in opposite directions.in opposite directions.

– Series of constructive Series of constructive and destructive and destructive interferences.interferences.

– They have regions of They have regions of no vibration (no vibration (nodesnodes) ) and regions of and regions of maximum vibration maximum vibration ((antinodesantinodes).).

Wave BehaviorWave Behavior• The frequency The frequency

of a wave can of a wave can change when change when the source of the source of the wave or the the wave or the observer is observer is moving. This is moving. This is called the called the Doppler Effect.Doppler Effect.