Chapter 12: Waves

Chapter 12:Waves

Section 12.1: WavesSection 12.2: Waves in Motion

Section 12.3: Natural Frequency and Resonance

Content Standard 3:Interaction of Energy and Matter

Energy, such as potential, kinetic, and field, interactswith matter and is transferred during these interactions.

1. All energy can be considered to be kinetic energy, which is energy of motion, potential energy, which depends on relative position; or energy contained by a field, such as electromagnetic waves.

2. Waves, includes sounds and seismic waves, waves over water, and light waves, have energy and can transfer energy when they interact with matter (such as used in telescope, solar power, and telecommunication technology)

Learning goals and VocabularyPage 194

Information on page 194 will be the responsibility of the student to read and have knowledge in order to succeed on the content exam.

Section 12.1: WavesPage 195

Why learn about waves?Waves carry oscillations from one place to anotherRefer to Figure 12.1 page 195 – ball in waterWaves carry information and energyWaves are used to carry informationand energy over great distances.


Why learn about waves? Continued…Waves are all around us.Refer to the examples on top of page196How do you recognize a wave?Students must know this list on pg. 196Where can we find waves?Refer to pg. 196 – bottom of page.


Transverse and longitudinal wavesWaves spread through connectionsA string is continuous because it isconnected to itselfTransverse wavesHas its oscillations perpendicular to thedirection the wave moves

Section 12.1: WavesPage 197 – continued …..

Transverse and longitudinal wavesLongitudinal wavesHas oscillations in the same direction asthe waves moves. Also known as acompression wave.Sound waves are good example of longitudinal waves.


Frequency, amplitudes and wavelengthBasic properties

FrequencyFrequency is measured in Hz

AmplitudeWavelength

SpeedThe speed of a wave

Section 12.1: WavesPage 198 : Basic Properties

Basic propertiesWaves have cycles, frequency and amplitude which were from chapter11.1.A new property will be the wavelength.

Section 12.1: WavesPage 198 : Frequency

FrequencyIs the measure how often the wavegoes up and down (Fig. 12.5)To measure the frequency, look at one place as the waves passes through.A wave carries its frequency to everyarea it reaches.

Section 12.1: WavesPage 198 : Frequency (Hz)

Frequency is measured in Hz.Is the measure how often the wavegoes up and down (Fig. 12.5)To measure the frequency, look at one place as the waves passes through.A wave carries its frequency to everyarea it reaches.

Section 12.1: WavesPage 198 : Amplitude

AmplitudeLearn some terms:Crest: highest part of a waveTrough: lowest part of a waveLine of origin: when a crest/trough isnot presentAmplitude: 2 amplitudes per cycle – refer to diagram drawn by instructor

Section 12.1: WavesPage 198 : Wavelength (m.)

WavelengthIs the length of one complete cycle of awave (Figure 12.7)The symbol “lambda” is used while the meter is the unit.Crest-to-crest or trough-trough.

Section 12.1: WavesPage 199 : Speed (m/s)

SpeedDescribes how fast the wave can transmit an oscillation from one place toanother.Refer to page 199 and the Skill Sheetfor more information.

Section 12.1: Waves Page 199 : What is the speed of a wave?

What is the speed of a wave?The speed of the wave is different from the speed of whatever the wave iscausing to move.Read the last sentence of the 2nd

paragraph on page 199

Section 12.1: Waves Page 199 : Speed is frequency times

wavelength

Speed is frequency times wavelengthIn one complete cycle, a wave moves forward one wavelength.

v = f λSpeed = frequency times wavelengthMeters/second = Hertz times metersRefer to page 199 and Skill Sheet for

further information.

Section 12.2 Waves in Motionpage 200

Wave shapesCrest, troughs, and wave frontsCrest - shape of the high points of thewaveTroughs – the low points of the waveWave fronts – crest is sometimereferred to as a wave front


Wave shapesPlane waves and circular wavesPlane waves – wave fronts that look likestraight lines. Wave is started by disturbing the water in a line.Circular waves – wave fronts thatappear circular. Wave is started by disturbing the water at a single point.


Wave shapesDetermining the direction the wavemovesDirection is determined by the shape:Plane waves have straight lines thatmove perpendicular to the wave fronts.Circular waves have circular wave frontsthat move outward from the center.


What happens when a wave hits something?The four wave interactionsReflectionRefractionDiffractionAbsorption


What happens when a wave hitssomething?BoundariesWaves are affected by boundarieswhere conditions change either crossingor at the boundary.


What happens when a wave hitssomething?Reflection – refer to page 201 for moreexamplesWhen a wave bounces off an obstacleand travel in another direction.Happens at a boundary (edge) wherethe wave has to pass from one conditionto another.


What happens when a wave hitssomething?RefractionThe wave starts in one direction andchanges direction as it crosses aboundary.Remember the pencil in the glass ofwater. Pencil appears to bend which is due tothe fact of the light changing from medium toanother.


What happens when a wave hitssomething?AbsorptionThe wave can be absorbed anddisappear.Absorption is what happens when theamplitude of a wave gets smaller and smalleras it passes through a material.


What happens when a wave hitssomething?DiffractionWaves can bend around obstacles andgo through openings.The wave is changed by passingthrough a hole or around an edge.

Section 12.3 Natural Frequency and Resonance page 203

Terms for Content Exam:a. Nodeb. Standingc. Anti-noded. Natural frequencye. Destructive interference


Natural frequencyWhat is natural frequency?The natural frequency is the frequencyat which a system oscillates when it isdisturbed.The pendulum also had a naturalfrequency.


Natural frequencyWhy natural frequency is important.The student needs to read the four reasons of natural frequency.


Natural frequencyChanging the natural frequencyThe natural frequency depends on manyfactors, such as the tightness, length, orweight of the string.Factors that affect natural frequencyinclude size, inertia, or forces on thesystem.


Resonance


Standing waves on a string


InterferenceInterference definedConstructive interferenceDestructive interference

TBW Chapter 12: Wavespages 207-209

Vocabulary Review – page 207Write questions and answers for all sets.Concept Review – page 208Write all questions and answers.Problems – page 209Write all questions and answers.

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Chapter 12: Waves