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Unit 7a: Wave PropertiesWaverepeating disturbance (oscillation or vibration) that transfers energy through matter or spaceWaves travel distances from a sourceMediumthe matter through which a wave movesElectromagnetic waves do not require a medium, but can travel through a vacuumMechanical wavesinvolve transfer of kinetic energy through matterThe medium does not travel with the wave, but the disturbance in the medium doesExample: A boat bobs up and down with the waves, but does not travel in the direction of the wave (very much) [test question?]Ocean waves and sound waves are mechanical wavesElectromagnetic waves are NOT mechanical wavesTransverse wavesParticles move in a direction perpendicular to the direction of wave travelExample: shaking a jump rope tied to a tree up and downImperfect example: ocean waves. There is some up and down movement, but there is also back and forth movement (compression) of water molecules.Longitudinal wavesParticles move back and forth along the same dimension the wave movesExamplesSound wavesholding several coils of a slinking (lying on a floor) together and letting goBoth water and seismic waves (earthquakes) can be examples of both types of wavesParts of a waveFor transverse waves, crests are high points of motion and troughs are low points.For longitudinal waves, a compression is where the particles are closest together, and a rarefaction (RAIR-e-faction) is the region where the particles are spread apart the most.WavelengthDistance from one region of a wave to the next occurrence of that region.For Transverse waves, wavelengths may be measured from crest to crest or trough to troughFor longitudinal waves, wavelengths may be measured from compression to compression or rarefaction to rarefaction.Periodamount of time, T, it takes for one wavelength to pass a point. It is measured in seconds.Frequencythe number of wavelengths that occur (vibrations) in one second. It is measured in Hertz (Hz) which is 1/s.the inverse of period (f = 1/T)Wave speedEquation: Speed (m/s) = frequency (in Hz) x wavelength (in m)v = f·λv = f·λfor a given wave, the higher the frequency, the lower the wavelengthdependent on medium and its conditions.sound waves travel faster in liquids than air. Sound travels faster in warmer air and slower in cooler air.Amplitudemeasure of the disturbance.Higher amplitude means higher energy transfer.In transverse waves, amplitude is crest height or trough depthIn longitudinal waves, amplitude is degree of compression—how close particles are togetherHigh amplitude sound waves = loudHigh amplitude light waves = brightHigh amplitude radio waves = good reception161544032067400High amplitude ocean waves = tsunamiName _______________________________________________ Date __________________ Due ___________________Wavelength, Frequency, and Speed PracticeSpeed of light = 2.998 x 108 m/s in a vacuumSpeed of sound = 340.29 m/s at sea level, dry air, 20C1. A student sends a wave of rope toward a tree to which it is tied. The crest-to-crest length is 0.65 m and 2.5 waves pass a point in 1 second. What is the speed of the waves in the rope?EquationRearrange (if needed)Plug inAnswer2. People have difficulty seeing colors with wavelengths beyond 740 nm (7.00 x 10-7 m). These colors are described as being infrared. What is the maximum frequency of infrared light?EquationRearrange (if needed)Plug inAnswer3. Most people cannot hear sounds below 20.0 Hz (although we can feel them). How long is the distance from compression to rarefaction of such a sound wave? (hint: how does compression to rarefaction length compare to wavelength?)EquationRearrange (if needed) Plug inAnswer4. (2pts) Many female pop stars can sing very high notes (pitch). Katy Perry can reach a pitch with a wavelength of 0.0370 m and Mariah Carey can reach a pitch with a wavelength of 0.0110 m. Christina Aguilera can reach a frequency of 2217 Hz, and Adele can reach 987.8 Hz. Order the pop stars in order of increasing high range. (Hint—there are two strategies to answer this)Strategy:Equations (rearrange if needed)Plug in:Answer and reasoning: ................
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