Lesson 2 Wave Properties

Chapter IntroductionLesson 1What arewaves?Lesson 2WavePropertiesLesson 3WaveInteractionsChapter Wrap-Up

How do wavestravel throughmatter?

What do you think?Before you begin, decide if you agree ordisagree with each of these statements.As you view this presentation, see if youchange your mind about any of thestatements.

Do you agree or disagree?1. Waves carry matter as they travelfrom one place to another.2. Sound waves can travel where thereis no matter.3. Waves that carry more energy causeparticles in a material to move agreater distance.

Do you agree or disagree?4. Sound waves travel fastest in gases,such as air.5. When light waves strike a mirror,they change direction.6. Light waves travel at the same speedin all materials.

What are waves? What is a wave? How do different types of waves makeparticles of matter move? Can waves travel through emptyspace?

What are waves? trough wave mechanical wave medium transverse wave crest longitudinalwave compression rarefaction electromagneticwave

What are waves? A wave is a disturbance that transfersenergy from one place to anotherwithout transferring matter. Waves transfer energy away from thesource of the energy. Waves leave matter in the same placeafter they pass.

What are waves? (cont.)What is a wave?

Water waves transfer energy across thepool, but not matter. As a result, the raftdoes not move along with the waves.

Water waves transfer energy across thepool, but not matter. As a result, the raftdoes not move along with the waves.

Mechanical Waves A wave that can travel only throughmatter is a mechanical wave. Mechanical waves cannot move througha vacuum. A material in which a mechanical wavetravels is called a medium.

Mechanical Waves (cont.) A transverse wave makes particlesin a medium move at right angles, orperpendicular, to the direction the wavetravels. The highest points on a transverse waveare crests. The lowest points on a transverse waveare troughs.

In a transverse wave, particles move atright angles to the direction the wavetravels.

Mechanical Waves (cont.)How do particles move ina transverse wave?

Mechanical Waves (cont.) A longitudinal wave makes the particlesin a medium move parallel to thedirection that the wave travels. The regions of a longitudinal wave wherethe particles in the medium are closesttogether are compressions. The regions of a longitudinal wave wherethe particles are farthest apart arerarefactions.

Longitudinal Waves

Longitudinal Waves

Mechanical Waves (cont.)How do particles move ina longitudinal wave?

Mechanical Waves (cont.) A vibration is a back-and-forth or anup-and-down movement of an object. Vibrating objects are the sources ofenergy that produce mechanical waves.

Vibrationsproduce wavesthat keep travelingeven when thevibrations stop.

Vibrationsproduce wavesthat keep travelingeven when thevibrations stop.

Types of Mechanical Waves All mechanical waves travel only inmatter. Sound waves and waves produced byearthquakes are mechanical waves thattravel in different mediums.

Electromagnetic WavesAn electromagnetic wave can travelthrough a vacuum and through matter.electromagneticfrom Greek elektron, means “amber”and magnes, means “lodestone”

Electromagnetic Waves (cont.)Light is an electromagnetic wave.Identify a type of wave that cantravel through a vacuum.

Electromagnetic Waves (cont.) Other types of electromagnetic wavesinclude radio waves, microwaves,infrared waves, and ultraviolet waves. Every object gives off electromagneticwaves. Humans and other objects near humanbody temperature also give off mostlyinfrared waves.

Electromagnetic Waves (cont.) Electromagnetic waves carry energy thatscientists call radiant energy. Infrared and visible light waves carryabout 92 percent of the radiant energythat reaches Earth from the Sun. Ultraviolet waves carry about 7 percentof the Sun’s energy.

Waves, such as those from a burningcandle, the Sun, or a loudspeaker,transfer energy away from the sourceof the wave. A transverse wave makes particles ina medium move at right angles to thedirectionof thewave.

A longitudinal wave makes theparticles in a medium move in adirection that is parallel to the directionthe wave travels.

Which term refers to the highestpoints on a transverse wave?A. troughB. rarefactionC. mediumD. crest

Which can be described as awave that can travel only throughmatter?A. transverse waveB. mechanical waveC. longitudinal waveD. electromagnetic wave

Which is the only type ofwave that can travel througha vacuum?A. electromagnetic waveB. longitudinal waveC. mechanical waveD. transverse wave

Do you agree or disagree?1. Waves carry matter as they travel fromone place to another.2. Sound waves can travel where there isno matter.

Wave Properties What are the properties of waves? How are the frequency and thewavelength of a wave related? What affects wave speed?

Wave Properties amplitude wavelength frequency

Amplitude and EnergyThe amplitude of a transverse wave is themaximum distance the particles in amedium move from their rest position asthe wave passes.amplitudefrom Latin amplitudinem,means “width”

The amplitude of a transverse wave isthe distance from the resting position to acrest or a trough.

The larger the amplitude, the more energythe wave carries.

The wave with the larger amplitude carriesmore energy and makes the ball bouncehigher.

Amplitude and Energy (cont.) The amplitude of a longitudinal wavedepends on the distance betweenparticles in the compressions andrarefactions. When the amplitude of a longitudinalwave increases, the particles in themedium get closer together in thecompressions and farther apart in therarefactions.

The amplitudeof a longitudinalwave on aspring dependson the spacingof the coils inthecompressionsandrarefactions.

Wavelength The wavelength of a wave is thedistance from one point on a waveto the nearest point just like it. Wavelength is measured in units ofdistance, such as meters.

To measure the wavelength of atransverse wave, you can measure thedistance from one crest to the next crest orfrom one trough to the next trough.

To measure the wavelength of alongitudinal wave, you can measure thedistance from one compression to the nextcompression or from one rarefaction to thenext rarefaction.

Frequency The frequency of a wave is the numberof wavelengths that pass by a point eachsecond. Frequency is related to how rapidly theobject or material producing the wavevibrates. Each vibration of the object producesone wavelength.

Frequency (cont.)What are the three propertiesof waves?

Frequency (cont.) The frequency of a wave is the same asthe number of vibrations the vibratingobject makes each second. The SI unit for frequency is hertz (Hz). To calculate the frequency of waves,divide the number of wavelengths by thetime. As the frequency of a wave increases,the wavelength decreases.

Frequency and Wavelength

Frequency (cont.)How does the wavelength changeif the frequency of a wavedecreases? What if the frequencyincreases?

Wave Speed Different types ofwaves travel atdifferent speeds. The same type ofwaves travel atdifferent speeds indifferent materials. Temperature alsoaffects the speed atwhich waves travel.

Wave Speed (cont.)What does wave speeddepend on?

Wave Speed (cont.)You can calculate the speed of a waveby multiplying its wavelength and itsfrequency together.

Wave Speed (cont.)

The amplitudeof a transversewave is themaximumdistance theparticles in amedium movefrom the restposition.

The wavelength of a transverse waveis the distancefrom one pointon a wave to thenearest pointjust like it, suchas from crestto crest or fromtrough to trough.

The wavelength of a longitudinal waveis the distance fromone point on awave to thenearest pointjust like it, suchas fromcompressionto compressionor fromrarefaction to rarefaction.

To measure the wavelengthof a transverse wave, you canmeasure the distance from onecrest to which of these?A. the next crestB. the next troughC. the next compressionD. the next rarefaction

Which refers to the number ofwavelengths that pass by a pointeach second?A. amplitudeB. compressionC. frequencyD. wavelength

What can you calculate bymultiplying wavelength andfrequency?A. amplitudeB. vibrationC. wave heightD. wave speed

Do you agree or disagree?3. Waves that carry more energy causeparticles in a material to move agreater distance.4. Sound waves travel fastest in gases,such as air.

Wave Interactions How do waves interact with matter? What are reflection, refraction, anddiffraction? What is interference?

Wave Interactions absorption refraction transmission diffraction reflection interference law of reflection

Interaction of Waves with Matter Waves can be reflected by matter or theycan change direction when they travelfrom one material to another. As waves pass through matter, some ofthe energy they carry can be transferredto matter.

Interaction of Waves with Matter (cont.) Absorption occurs whenenergy carried by a wavetransfers to the material inwhich it is traveling. The amount of energy absorbeddepends on the type of wave and thematerial in which it moves. All materials absorb electromagneticwaves, although some materials absorbmore electromagnetic waves than others.

Interaction of Waves with Matter (cont.)Transmission occurs when waves passthrough a material.

Interaction of Waves with Matter (cont.) Reflection occurs whenwaves bounce off thesurface of a material. An object that reflects allvisible light would appear white,while an object that reflects no visiblelight would appear black. All types of waves, including soundwaves, light waves, and water waves,can reflect when they hit a surface.

Interaction of Waves with Matter (cont.)What are three ways that wavesinteract with matter?

The Law of Reflection A line that is perpendicular to a surface iscalled the normal. The angle between the direction of theincoming wave and the normal is theangle of incidence. According to the law of reflection, theangle between the direction of thereflected wave and the normal is theangle of reflection.

According to the law of reflection, theangle of incidence equals the angle ofreflection for all waves.

The Law of Reflection (cont.)normalScience Use perpendicular to orforming a right angle with a line orplaneCommon Use conforming to astandard or common

Refraction Sometimes waves change direction evenif they are not reflected from a surface. Refraction occurs when a wavechanges direction because its speedchanges. The greater the change in speed, themore the wave changes direction.

The beam of light changes directionbecause light waves slow down as theymove from air into water.

Refraction (cont.)refractionfrom Latin refractus, means“to break up”

Diffraction Waves can change direction as theytravel by objects. The change in direction of a wave whenit travels by the edge of an object orthrough an opening is called diffraction. The wavelengths of sound waves aresimilar in size to many common objects.

Diffraction (cont.)Compare and contrast reflection,refraction, and diffraction.

Interference In addition to interacting with matter,waves also interact with each other. Interference occurs when waves thatoverlap combine to form a new wave. After waves travel through each other,they keep moving without having beenchanged.

Wave InterferenceWhen waves interfere with each other,they create a new wave that has a differentamplitude than either original wave.

Wave Interference

Interference (cont.) As waves travel through each other,sometimes the crests of both wavesoverlap, forming a new wave with greateramplitude than either of the originalwaves. This type of interference is calledconstructive interference.

Interference (cont.) Destructive interference occurs when acrest of one wave overlaps the trough ofanother wave. The new wave that forms has a smalleramplitude than the sum of theamplitudes of the original waves.

Interference (cont.)Describe two types of waveinterference.

Transmission occurswhen waves travelthrough a material.