Chapter 16 Temperature and Heat

1. Chapter 16 Temperature and Heat

2. Temperature and the Zeroth Law of Thermodynamics Definition of heat: Heat is the energy transferred between objects because of a temperature difference. Objects are in thermal contact if heat can flow between them. When the transfer of heat between objects in thermal contact ceases, they are in thermal equilibrium.

3. Temperature Scales The three temperature scales compared:

4. Thermal Expansion • Most substances expand when heated; the change in length or volume is typically proportional to the change in temperature. • The proportionality constant is called the coefficient of linear expansion.

5. 16-3 Thermal Expansion Some typical coefficients of thermal expansion: Table 16-1

6. Thermal Expansion The expansion of an area of a flat substance is derived from the linear expansion in both directions: Holes expand as well:

7. Heat and Mechanical Work Experimental work has shown that heat is another form of energy. James Joule used a device similar to this one to measure the mechanical equivalent of heat:

8. 16-4 Heat and Mechanical Work One kilocalorie (kcal) is defined as the amount of heat needed to raise the temperature of 1 kg of water from 14.5° C to 15.5° C. Through experiments such as Joule’s, it was possible to find the mechanical equivalent:

9. Specific Heats The heat capacity of an object is the amount of heat added to it divided by its rise in temperature: Q is positive if ΔT is positive; that is, if heat is added to a system. Q is negative if ΔT is negative; that is, if heat is removed from a system. A quantity which is a property only of the material (mass) is the specific heat:

10. Conduction, Convection, and Radiation Conduction, convection, and radiation are three ways that heat can be exchanged. Conduction is the flow of heat directly through a physical material.

11. Conduction, Convection, and Radiation • Conduction: heat exchange from one part of a material to a cooler part, with no bulk motion of the material. • Experimentally, it is found that the amount of heat Q that flows through a rod: • increases proportionally to the cross-sectional area A • increases proportionally to the temperature difference from one end to the other • increases steadily with time • decreases with the length of the rod The constant k is called the thermal conductivity of the rod. Table 16-3

12. Conduction, Convection, and Radiation Some typical thermal conductivities: Substances with high thermal conductivities are good conductors of heat; those with low thermal conductivities are good insulators.

13. Conduction, Convection, and Radiation Convection is the flow of fluid due to a difference in temperatures, such as warm air rising. The fluid “carries” the heat with it as it moves. • Convection is heat exchange due to the bulk motion of an unevenly heated fluid. • Radiation is heat exchange due to electromagnetic radiation.

14. AP PHYSICS B Please read the Chapter 16 Summary. WA 16.1, Text Problems 18, 33,49,52 Workday Blended Thursday – Go over WA 16.1 Quiz 16 only Friday or Monday? Chapter 17,18 Start on Monday.