Loudoun County Public Schools / Overview



Waves, Chapter 20 (PS 8 & 9)Name ___________________________________________Section 20-1VocabularyExplanationDrawing/ExampleWavecan be mechanical or electromagneticA disturbance that transmits ENERGY (not matter!) through SPACE and/or MATTER.To make the wave travel further, it has to have more ENERGY. (Think of yelling!)Examples: LIGHT, SOUND, OCEANMediumA SUBSTANCE the wave travels through, such as SOLIDS, LIQUIDS OR GAS.The matter DOES NOT move with the wave, just the ENERGY!Think about solids/liquid/gas particle arrangementMechanical Wave (type)(matter & medium)= m & m’sRequire a MEDIUMParticles bump particles to transmit energyEx: DOMINOES HITTING DOMINOES… CARRIES ENERGY, BUT NOT THE DOMINOExamples: SOUND, WATERElectromagnetic Wave (type)Do not require a MEDIUMEM (ElectroMagnetic) SPECTRUM Examples: LIGHT WAVES (microwaves, radio, light, xray)TransverseAll transverse! Waves in which particles vibrate with an UP & DOWN MOTION and the particles move PERPENDICULAR to the direction the wave is traveling.Require a medium? NOExamples: EM WAVESCompression / Longitudinal(make graphic organizer now)Waves in which particles of the MEDIUM vibrate BACK & FORTH (particles bump barticles) along the path the wave travels. (and repeat pattern)Require a medium? YESExamples: SOUNDCrestThe HIGHEST point of a TRANSVERSE waveTroughThe LOWEST point of a TRANSVERSE waveCompressionThe area where the PARTICLES of the wave CROWD TOGETHER for a COMPRESSION (longitudinal) waveRarefaction(label wave diagrams now)The area of where the PARTICLES of the wave SPREAD APART for a COMPRESSION (longitudinal) waveSection 20-1 ReviewA wave is a DISTURBANCE that carries ENRGY. A wave can travel through MATTER or SPACE. There are two kinds of waves we’ve discussed: waves that require a medium called MECHANICAL or waves that do not require a medium called ELECTROMAGNETIC. The TRANSVERSE waves have crests and troughs and are the ELECTROMAGNETIC waves. The COMPRESSION (or LONGITUDINAL) waves have compressions and rarefactions are the MECHANICAL waves.Section 20-2VocabularyExplanationDrawing/ExampleWave Velocity/Speed (v)Measured in m/s. Velocity depends on the MEDIUM for a compression wave. V = λ x f (put in triangle w/ units)Think of velocity due to medium… Frequency (f)The number of WAVES produced in a given amount of TIME (how many WAVES pass each SECOND)Count the number of CRESTS or TROUGHS for a transverse wave or the number of COMPRESSIONS or RAREFACTIONS for a compression/longitudinal wave that pass by each second.The higher the frequency, the SHORTER the wavelength and the ( less / more ) energy.Hertz (Hz)The unit used to measure FREQUENCY: 1 Hz = 1 WAVE/SECONDWavelength( λ )Unit: metersThe DISTANCE between two adjacent CRESTS or TROUGHS for a transverse wave or the distance between two adjacent COMPRESSIONS or RAREFACTIONS for a compression/longitudinal waveλ and f have INVERSE relationshipAmplitude(m)The MAXIMUM distance a wave vibrates from the REST POSITION (also called equilibrium).(1/2 the “height” of the wave)The larger the amplitude, the ( less / more ) energy.bottom pic has most energy due to highest amplitude215901270Section 20-2 ReviewThere are four properties of waves: wave velocity measured by m/s, frequency measured in HERTZ (Hz), wavelength measured in METERS and amplitude measured in METERS. The speed of a wave is determined by the MEDIUM the wave is traveling through. If wavelength increases, frequency DECREASES. Section 20-3VocabularyExplanationDrawing/ExampleReflectionThe BOUNCING BACK of a wave after it hits a BARRIER or an objectExample: echo, sonar, ultrasoundRefractionThe BENDING of a wave as it passes at an ANGLE from one MEDIUM to another due to the difference in WAVE SPEED (velocity) in the mediums.21590-3810Example: straw in glass of waterDiffractionThe BENDING of waves around a BARRIER or through an OPENING and is determined by the WAVELENGTH and/or the size of the BARRIER. (= new waves produced)Example: light coming into dark room from hallway or hearing sounds from locker area in classroomInterferenceThe result of two or move waves OVERLAPPING (as a result of diffraction). 3 Types: CONSTRUCTIVE, DESTRUCTIVE OR RESONANCEExample: PEOPLE TALKING AT SAME TIMEConstructive InterferenceWhen one wave OVERLAPS another wave.This results in (smaller/larger) amplitudes, which means MORE energy or LOUDER sounds. (or brighter light)Example: band vs soloist or one candle vs severalDestructive InterferenceWhen one wave OVERLAPS another wave. This results in (smaller/larger) amplitudes, which means LESS energy or SOFTER sounds. Or dimmer lightTwo waves with identical amplitudes will CANCEL EACH OTHER. = SILENCEExample: sometimes happens in orchestra halls = dead/silence spotsNoise cancelling headphonesResonanceWhat occurs when an object vibrating at or near the RESONANT FREQUENCY of a second object causes the second object to VIBRATE.(They vibrate at maximum amplitude at certain frequencies.)Example: your car shakes due to car next to you having thumping stereoOr making sound from rubbing rim of water glassSection 20-3 ReviewThere are four wave interactions: REFLECTION, REFRACTION, DIFFRACTION or INTERFERENCE. Seeing myself in the mirror is an example of REFLECTION and seeing light come into a dark room from a hallway is an example of DIFFRACTION. When waves overlap and become louder, we call it CONSTRUCTIVE interference. When one object vibration causes another object to vibrate, we call that RESONANCE. ................
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