Temperature, Heat, and Thermal Energy: Concepts and Applications

1. Chapter 12 Temperature and Heat Chapter 13 The Transfer of Heat

2. William Thomson (Lord Kelvin)(1824 - 1907) Temperature • Thermodynamics – branch of physics studying thermal energy of systems • Temperature (T), a scalar – measure of the thermal (internal) energy of a system • SI unit: K (Kelvin) • Kelvin scale has a lower limit (absolute zero) and has no upper limit

3. Kelvin scale • Kelvin scale is defined by the temperature of the triple point of pure water • Triple point – set of pressure and temperature values at which solid, liquid, and gas phases can coexist • International convention: T of the triple point of water is

4. The zeroth law of thermodynamics • If two (or more) bodies in contact don’t change their internal energy with time, they are in thermal equilibrium • 0th law of thermodynamics: if bodies are in thermal equilibrium, their temperatures are equal

5. Measuring temperature • Temperature measurement principle: if bodies A and B are each in thermal equilibrium with a third body C, then A and B are in thermal equilibrium with each other (and their temperatures are equal) • The standard temperature for the Kelvin scale is measured by the constant-volume gas thermometer

6. Constant-volume gas thermometer

7. Anders Cornelius Celsius (1701 - 1744) Gabriel Daniel Fahrenheit (1686 - 1736) Celsius and Fahrenheit scales • Celsius scale: • Fahrenheit scale:

8. Chapter 12 Problem 8 If a nonhuman civilization were to develop on Saturn’s largest moon, Titan, its scientists might well devise a temperature scale based on the properties of methane, which is much more abundant on the surface than water is. Methane freezes at -182.6 °C on Titan, and boils at -155.2 °C. Taking the boiling point of methane as 100.0 °M (degrees Methane) and its freezing point as 0 °M, what temperature on the Methane scale corresponds to the absolute zero point of the Kelvin scale?

9. Thermal expansion • Thermal expansion: increase in size with an increase of a temperature • Linear expansion: • Volume expansion:

10. Thermal expansion

11. Chapter 12 Problem 21 A simple pendulum consists of a ball connected to one end of a thin brass wire. The period of the pendulum is 2.0000 s. The temperature rises by 140 °C, and the length of the wire increases. Determine the period of the heated pendulum.

12. Temperature and heat • Heat (Q): energy transferred between a system and its environment because of a temperature difference that exists between them • SI Unit: Joule • Alternative unit: calorie (cal):

13. Q Q Absorption of heat • Specific heat (c): heat capacity per unit mass • Common states (phases) of matter: solid, liquid, gas • Latenet heat (L): the amount of energy per unit mass transferred during a phase change (boiling, condensation, melting, freezing, etc.)

14. Q Q Absorption of heat

15. Absorption of heat

16. Absorption of heat

17. Chapter 12 Problem 55 A rock of mass 0.20 kg falls from rest from a height of 15 m into a pail containing 0.35 kg of water. The rock and water have the same initial temperature. The specific heat capacity of the rock is 1840 J/(kg × C°). Ignore the heat absorbed by the pail itself, and determine the rise in the temperature of the rock and water.

18. Chapter 12 Problem 69 An unknown material has a normal melting/freezing point of -25.0 °C, and the liquid phase has a specific heat capacity of 160 J/(kg × C°). One-tenth of a kilogram of the solid at -25.0 °C is put into a 0.150-kg aluminum calorimeter cup that contains 0.100 kg of glycerin. The temperature of the cup and the glycerin is initially 27.0 °C. All the unknown material melts, and the final temperature at equilibrium is 20.0 °C. The calorimeter neither loses energy to nor gains energy from the external environment. What is the latent heat of fusion of the unknown material?

19. Thermal conductivity Heat transfer mechanisms • Thermal conduction • Conduction rate: • Thermal resistance: • Conduction through a composite rod:

20. Heat transfer mechanisms

21. Chapter 13 Problem 15 A pot of water is boiling under one atmosphere of pressure. Assume that heat enters the pot only through its bottom, which is copper and rests on a heating element. In two minutes, the mass of water boiled away is m = 0.45 kg. The radius of the pot bottom is R = 6.5 cm, and the thickness is L = 2.0 mm. What is the temperature TE of the heating element in contact with the pot?

22. Emissivity Josef Stefan (1835-1893) Heat transfer mechanisms • Thermal radiation • Radiation rate: • Stefan-Boltzmann constant: • Absorption rate:

23. Chapter 13 Problem 31 Liquid helium is stored at its boiling-point temperature of 4.2 K in a spherical container (r = 0.30 m). The container is a perfect blackbody radiator. The container is surrounded by a spherical shield whose temperature is 77 K. A vacuum exists in the space between the container and the shield. The latent heat of vaporization for helium is 2.1 × 104 J/kg. What mass of liquid helium boils away through a venting valve in one hour?

24. Heat transfer mechanisms • Convection

25. Heat transfer mechanisms

26. Questions?