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This 4 page Class Notes was uploaded by Oreofeoluwa on Sunday September 13, 2015. The Class Notes belongs to PHYS1033 at University of Cincinnati taught by Dr. Howard Jackson in Fall 2015. Since its upload, it has received 41 views. For similar materials see Physics of Sound and Music in Physics 2 at University of Cincinnati.
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Date Created: 09/13/15
PHY51033001 Oreofeoluwa Oyelowo PHYS 1033 Physics of Sound and Music Dr Howard Jackson Week 3 Waves Longitudinal waves transverse waves beats the Doppler effect ultrasonics WAVES Properties of a wave 1 A wave is a disturbance within a medium the disturbance travels propagates at a certain velocity which depends on the medium 2 A wave transfers energy as it moves from its source to its destination and this allows it to do work A typical example is the sun waves which supply heat and light to the earth 21 Transverse and Longitudinal Waves There are two basic types of waves transverse and longitudinal waves The difference between them is seen in the direction of the wave motion relative to the direction of propagation of the wave Transverse wave displacement is perpendicular to the line of propagation When this motion is plotted on a graph it looks like a sine wave Examples are electromagnetic waves light waves and slinky spring waves created by moving the springs up and down while this motion travels down the spring The motion here up or down is perpendicular to the line of propagation Longitudinal wave displacement is along the line of propagation Examples are sound waves and slinky spring waves that are created by compressing the spring at a point We see as the wave is transmitted down to the end of the spring and back Recall group experiment in class to demonstrate a longitudinal wave For the purpose of this class we would be looking at sound waves There are 4 major characteristics of sound waves 1 It is a longitudinal wave with frequencies ranging between 20Hz and 20kHz 2 It requires a medium Recall bell in a vacuum experiment 3 It is created by mechanical vibration Recall candle in front of a speaker experiment 4 It travels at a particular speed Recall that the speed of sound is NOT constant but depends on temperature Speed of sound 3313 06 X Temperature in Celsius llPage PHY51033001 Oreofeoluwa Oyelowo Fundamental Properties of Waves 1 Huygen s Principle closely tied with diffraction 2 Superposition You know how we are told that matter is anything that has mass and occupied space And that no two bodies can occupy the same position at the same time Well that s not true when we are talking about WAVES Because two waves can occupy the same position at the exact same time without affecting each other Waves can also pass THROUGH each other without affecting each other That being said we can state the law ofsuperposition in any of the following ways a Two waves can coexist without affecting each other even if they are in the same place at the same time b Waves add up algebraically We also explain superposition in terms of the algebraic addition of waves You know how two forces can act on a body at the same time and the resultant force is the addition of both individual forces acting on the body Waves work the same way We will visit more on that later This will be used to explain the principle of interference and addition of waves 3 Inverse Square Law The farther one goes from a source of sound the softer it sounds and the more intensely the sound has to be produced for it to be heard at the same volumeloudness This principle explains how the intensity of a sound decreases as the observer gets closer to the source of the sound It is explained with the formula below 0lt L r2 where I intensity and r distance between the source and observer This explain the inverse proportionality relationship showing that the intensity increases as the distance reduces and vice versa 4 Polarization This property is unique to transverse waves If we can cause all the waves to get propagated in one direction then we can say that the waves are polarized We see this application in polarizing sunglasses Beats If we add two waves of different frequencies we hear a resulting frequency that is the average of the two frequencies that we added ZlPage PHY51033001 Oreofeoluwa Oyelowo Fhear fl f2 2 We also have what we call intensity variation which is the positive difference between both frequencies We cannot have negative values for that The Doppler Effect This compares the differences in the frequency of the sound we hear with the distance of the observer Let us consider the experiment Professor Jackson carried out in class with a ball that produced a sound at a particular frequency As he threw the ball to a person at the back of the class those closer to the back heard a higher pitch as the ball was getting closer to them and those sitting closer to the front of the class heard a lower pitch as the ball got farther away from them Also as an observer standing stationary you hear an ambulance approaching from a distance The frequency you hear is higher as the ambulance gets closer to you and as the ambulance gets farther away There is a formula we use to calculate the frequency of sound we hear as a result of the Doppler Effect Fhear f0 S S V0 Where fo frequency of source S velocity of sound and V0 spend of source Fhear fsource Vsound Vsound 39 Vsource For a sound that is moving away from you Fhear fsource Vsound Vsound Vsource Ultrasonics The frequency of human hearing is 20Hz to 20kHz Waves that have a frequency that is less than 20Hz are called infrasonics Waves that have a frequency that is greater than 20kHz are called ultrasonics Ultrasound is useful in the following ways Measuring the depths of oceans and lakes 7 a 7 39 Lg quot PHY51033001 Oreofeoluwa Oyelowo Locate and track submarines underwater Locate mines under water Medical diagnostics 0 Measure blood flow 0 The most popular making sonograms ultrasonic pictures of the fetus at various stages of pregnancy Medical surgeries such as 0 Breaking up kidney stones 4Page