1Phys 1240: Sound and Musicwww.colorado.edu/physics/phys1240LAST: waves and oscillationsTODAY: more on wavesNEXT: waves and simple harmonicmotionREAD: Start Ch 3, up to 3.1Study session tomorrow at 7(plus lots of office hours, andessentially all Thursday afternoon!)Emailed CAPA long answer scores• Do you have an electric guitaryou can bring to class?• Do you have a “practice violin”(with no resonating box) youcan bring to class?• Do you have a “reedinstrument” mouthpiece youcan bring to class?Let me know, these would befun for a quick demo onThursday or next Tues!CT 1.3.4xTransverse and longitudinal• Which one of the following ismost likely to be impossible?A: Transverse waves in a gasB: Longitudinal waves in a gasC: Transverse waves in a solidD: Longitudinal waves in a solidE: They all seem perfectly possibleSpeed of sound(344 m/s)Clap => travels 3.26 m down a tube, echoes off the end and returnsHow much time elapses?What would an oscilloscopetrace look like? (pressure vs time?)2I grab the left end of a LONG string andwiggle it up and down.Traveling wave on a stringVarious ways to represent thistraveling wave: displacementtimeI grab the left end of a LONG string andwiggle it up and down.Traveling wave on a stringVarious ways to represent thistraveling wave: displacementx(position)I grab the left end of a LONG string andwiggle it up and down.Traveling wave on a stringVarious ways to represent thistraveling wave: displacementx(position)I grab the left end of a LONG string andwiggle it up and down. There is a purplepainted spot somewhere on the string.What choice below best shows the motionof the purple spot?A) (up and down)B) (pushed steadily to the right)C) (left and right)D) (no motion)E) (circular path)CT 1.3.3x3The speaker moves back and forth at a constantrate, creating a loud steady sound waveVarious ways to represent thissound wave:speakerSound waves λThe speaker moves back and forth at aconstant rate, creating a loud sound waveVarious ways to represent thissound wave:speakerSound wavesThe speaker moves back and forth at aconstant rate, creating a loud sound waveVarious ways to represent thissound wave:speakerSound wavesThe speaker moves back and forth at aconstant rate, creating a loud sound waveVarious ways to represent thissound wave:speakerSound waves4A dust particle is located in front of aspeaker. The speaker moves back and forth ata constant rate, creating a loud sound wave.Which choice below shows the motion of thedust particle?speakerdustCT 1.3.2xA) (up and down)B) (pushed steadily to the right)C) (left and right)D) (no motion)E) (circular path)Evidence forlongitudinal sound waveA key relationship!Speed = distance / time takenFor all traveling waves, if the wavewiggles at frequency f, the periodP = 1/fTo travel ONE wavelength takesONE period.Speed = wavelength / period = wavelength * frequency = λ fV = λ f Wave simCT 2.1.5You are standing outside on a pleasant fallday, playing a recorder. You play “concertA”, also known as A440 (i.e. during onesecond 440 compressions of air moveoutwards).What is the approximate wavelength of thesound wave?(Recall: the speed of sound is 344 m/s)a) A couple of mmb) Close to a kmc) A little over one meterd) A little under one metere) None of the above* (Do you know this instrument?).5CT 2.1.6The air warms up by 20o C. It turns out thatthis instrument (like most wind instruments)produces waves of a particular wavelength.So, changing the temperature will notchange the wavelength of sound wavesproduced (noticeably.)What will change?a) Frequencyb) Speedc) Bothd) Neithere)
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