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,  = 90 dB  = (10 dB) log (I/I 0 ) 10 (  /10) = I/I 0 I = I 0 10 (  /10) I = ( ) 10 (90/10) We need to relate I to s m : I = ½  v  2 s m 2 s m = (I/½  v  2 ) ½  Air density =  =  Velocity of sound = v = 343 m/s

PAL #9 Music (cont.) s m = (I/(½  v(2  f) 2 )) ½ s m = (1X10 -3 /(½)(1.21)(343)(2  256) 2 ) ½ s m =  Even the loudest sounds only produce very small motions  What if the distance is doubled?  Since I = P s /4  r 2, then I 2 = (1/4)I 1   The displacement is ½ as great

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

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”

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

Heat Units  Heat is a form of energy and so its SI unit is the joule (kg m 2 /s 2 )  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) 

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

Temperature Scales  Celsius scale   Kelvin scale   The Kelvin scale is designed so that 0 K is at absolute zero and that K is at the freezing point of water  T C = T K T F = 9/5 T C +32

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 degrees Celsius is the coldest it can get

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

Linear Expansion   L = L   T  Where  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

Volume Expansion   V = V   T  Where  =3    Density (in general) decreases with increasing temperature  This is what makes a hot air balloon work

Next Time  Read:

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? a)Larger than 440 Hz b)Smaller than 440 Hz c)The same as 440 Hz

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? a)Larger than 440 Hz b)Smaller than 440 Hz c)The same as 440 Hz

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? a)Larger than 440 Hz b)Smaller than 440 Hz c)The same as 440 Hz

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? a)Larger than 440 Hz b)Smaller than 440 Hz c)The same as 440 Hz