1. Temperature Physics 202 Professor Lee Carkner Lecture 12

2. PAL # 11 Doppler b)Detector toward, Source toward: f’ = f ( v+v D / v-v S ) for v D = 3 m/s, f’ higher d) Detector away, Source toward: f’ = f ( v-v D / v-v S ) for v D = 3 m/s, f’=f c) Detector away, Source away: f’ = f ( v-v D / v+v S ) for v D = 3 m/s, f’ lower e) Detector toward, Source away: f’ = f ( v+v D / v+v S ) for v D = 3 m/s, f’=f

3. Thermodynamics    Thermodynamics deals with the internal energy of a system   We will examine how this internal energy changes due to changes in heat and work  One of the important concepts in thermodynamics is temperature   How do we experience temperature?

4. Thermoscope  Changes in temperature cause changes in other properties     We can measure these changes to construct a thermoscope, a device to record changes in temperature   The oven is at a higher temperature than the refrigerator  Temperature changes are caused by an exchange of heat

5. A Thermoscope

6. Thermal Equilibrium   When the thermoscope stops changing, it and the water are in thermal equilibrium    If we move the thermoscope to a different cup and it reads the same value we know that it and the second cup are also in thermal equilibrium

7. Zeroth Law of Thermodynamics  What happens if we pour the two cups together?   The cups are in thermodynamic equilibrium with each other  If two objects are each in thermal equilibrium with a third object then they are also in thermal equilibrium with each other

8. How Thermal Equilibrium Works

9. Thermometers   In order for a thermoscope to be a thermometer if needs to be calibrated  For example, the Celsius scale   Them put the tube in boiling water and mark that mercury level “100”   You now have a Celsius thermometer

10. The 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  T C = T K -273.15

11. The Triple Point of Water   The triple point of water is the only temperature where water can exist in liquid, solid and gas forms simultaneously 

12. Converting Temperatures  A temperature change of 5 Celsius degrees is equal to a temperature change of 9 Fahrenheit degrees

13. 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

14. Three Temperature Scales

15. What’s Hot, What’s Not

16. 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

17. Thermal Expansion of Ruler

18. Linear Expansion  The degree to which the length of an object changes is given by:  L = L   T   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

19. Bimetal Strip

20. Volume Expansion  If the linear dimensions of a solid change then the volume must change:   Where  =3    Density in general decreases with increasing temperature 

21. 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   Being “hot” does not mean you have a lot of “heat”

22. 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 

23. What is Heat?

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