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Temperature

Temperature. Physics 202 Professor Lee Carkner Lecture 10. PAL #9 Music. How much would your eardrum move from a tuning fork sound? Example: f = 256 Hz, b = 90 dB b = (10 dB) log (I/I 0 ) 10 ( b /10) = I/I 0 I = I 0 10 ( b /10) I = (10 -12 ) 10 (90/10)

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Temperature

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  1. Temperature Physics 202 Professor Lee Carkner Lecture 10

  2. PAL #9 Music • How much would your eardrum move from a tuning fork sound? • Example: f = 256 Hz, b = 90 dB b = (10 dB) log (I/I0) 10(b/10) = I/I0 I = I0 10(b/10) I = (10-12) 10(90/10) We need to relate I to sm: I = ½ rvw2sm2 sm = (I/½rvw2)½ • Air density = r = • Velocity of sound = v = 343 m/s

  3. PAL #9 Music (cont.) sm = (I/(½ rv(2pf)2))½ sm = (1X10-3/(½)(1.21)(343)(2p256)2)½ sm = • Even the loudest sounds only produce very small motions • What if the distance is doubled? • Since I = Ps/4pr2, then I2 = (1/4)I1 • The displacement is ½ as great

  4. Thermodynamics • Energy we have known: • Kinetic energy • Potential energy • Thermodynamics deals with the internal energy of a system • We will examine how this internal energy changes due to heat and work • Temperature is a measure of an object’s internal energy

  5. Temperature and Heat • Temperature is a measure of the internal (thermal) energy of a system • Heat (Q) is energy transferred between systems due to a temperature difference • Heat can manifest itself in different ways • Heat is not a thing or a condition • Being “hot” does not mean you have a lot of “heat”

  6. Heat • The rate of heat exchange depends on the temperature difference • Run warm water over your hands after being outside on a cold day and the water feels hot • You feel hot on a hot day because your body generates heat and can’t get rid of it quickly enough • Small temperature difference, low heat flow

  7. Heat Units • Heat is a form of energy and so its SI unit is the joule (kg m2/s2) • 1 joule (J) = • A joule is fairly small so sometimes the kilojoule (kJ) is used • 1 calorie is the heat needed to raise the temperature of 1 gram of water 1 deg C • 1 cal = • The nutritional Calorie = 1000 standard calories (1 Cal = 1 kilocal)

  8. Thermal Equilibrium • Heat is energy transfer due to a difference in temperature • Put a thermometer in a cup of water, when it stops changing, it and the water are in thermal equilibrium • They are at the same temperature • Zeroth Law of Thermodynamics • If two objects are each in thermal equilibrium with a third object then they are also in thermal equilibrium with each other

  9. Temperature Scales • Celsius scale • Kelvin scale • The Kelvin scale is designed so that 0 K is at absolute zero and that 273.15 K is at the freezing point of water TC = TK -273.15 TF = 9/5 TC +32

  10. Temperature Scales • Gabriel Daniel Fahrenheit invented the mercury thermometer in 1714 • Anders Celsius introduced his scale is 1742 • William Thomson, Lord Kelvin, determined from theory that minus 273.15 degrees Celsius is the coldest it can get

  11. Thermal Expansion • Some objects expand more than others when heated • The degree of expansion depends on the change in temperature and the coefficient of expansion

  12. Linear Expansion DL = L aDT • Where a is the coefficient of linear expansion • This applies to all dimensions of a solid length, width and height • Two strips of metal with different coefficients of linear expansion attached together • This principle is used in dial thermometers and thermostats

  13. Volume Expansion DV = V bDT • Where b=3a • Density (in general) decreases with increasing temperature • This is what makes a hot air balloon work

  14. Next Time • Read: 18.7-18.10

  15. Car 1 on the left has a trumpet player on it playing “A” (440 Hz) and is moving at 3 m/s. Car 2 on the right has a tape recorder on it and is moving at 2 m/s. What is the recorded frequency when the trumpeter moves to the right and the recorder moves to the left? • Larger than 440 Hz • Smaller than 440 Hz • The same as 440 Hz

  16. Car 1 on the left has a trumpet player on it playing “A” (440 Hz) and is moving at 3 m/s. Car 2 on the right has a tape recorder on it and is moving at 2 m/s. What is the recorded frequency when the trumpeter moves to the left and the recorder moves to the right? • Larger than 440 Hz • Smaller than 440 Hz • The same as 440 Hz

  17. Car 1 on the left has a trumpet player on it playing “A” (440 Hz) and is moving at 3 m/s. Car 2 on the right has a tape recorder on it and is moving at 2 m/s. What is the recorded frequency when the trumpeter moves to the right and the recorder moves to the right? • Larger than 440 Hz • Smaller than 440 Hz • The same as 440 Hz

  18. Car 1 on the left has a trumpet player on it playing “A” (440 Hz) and is moving at 3 m/s. Car 2 on the right has a tape recorder on it and is moving at 2 m/s. What is the recorded frequency when the trumpeter moves to the left and the recorder moves to the left? • Larger than 440 Hz • Smaller than 440 Hz • The same as 440 Hz

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