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Thermal Physics

Thermal Physics. Lesson 3A Basic Thermal Concepts. ?. ?. ?. ?. ?. ?. ?. ?. ?. ?. ?. Temperature. The degree of “hotness” of a substance. Indicates the direction of flow of “hotness” . “Hotness” flows from HOT to COLD. HOT. COLD. Temperature.

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Thermal Physics

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  1. Thermal Physics Lesson 3A Basic Thermal Concepts

  2. ? ? ? ? ? ? ? ? ? ? ?

  3. Temperature • The degree of “hotness” of a substance. • Indicates the direction of flow of “hotness”. “Hotness” flows from HOT to COLD HOT COLD

  4. Temperature • A measure of the average random kinetic energy of the particles in a substance. N.B.Particles don’t all have the same speed!

  5. Temperature • The higher the temperature, the higher the average speed of the particles. N.B.Particles don’t all have the same speed!

  6. Thermal Energy • Energy (in J) transferred between bodies as a result of a temperature gradient. • Commonly referred to as heat. • High temperature is not the same as high heat! • A sparkler’s sparks are800 C but are harmless • A cup of tea is near 100 Cbut can burn you badly

  7. Modes of Heat Transfer • Conduction • Collisions between atomsor molecules. • Convection • Bulk movement of matterfrom one place to another. • Radiation • Transmission of energyin the form of light.

  8. Thermal Equilibrium • Consider bodies brought into thermal contact: • Eventually, a steady state is reached: HOT HOT COLD COLD WARM WARM

  9. Thermal Equilibrium • A state in which there is no net transferof thermal energy; temperatures are equal. • At the molecular level, thermal equilibrium occurs when the rates of thermal energy transfer between bodies are equal. WARM WARM

  10. Examples of Thermal Equilibrium • Cooling of a cup of tea • Thawing food in water • Getting into a cold bed • CSI - time of death • . . . • Using a thermometer!

  11. Measuring Temperature

  12. Measuring Temperature • Scientists noted that changes in temperature cause changes in volume. What then? • Build a device that indicatesthe changes in volume. • Observe that some eventsalways seem to occur at fixed temperatures. COLD HOT

  13. Measuring Temperature • Pick at least two fixed temperatures: • The melting/boiling points of H2O. • The sublimation point of CO2. • The boiling point of titanium. • Define a scale between them: • Fahrenheit (1724) • Celsius (1742) • Kelvin (1848, 1954)

  14. Temperature Scales • Celsius • MP of H2O = 0 C • BP of H2O = 100 C • Fahrenheit • MP of H2O = 32 F • BP of H2O = 212 F • Kelvin • Absolute zero = 0 K • Triple point of H2O = 273.16 K • Relationships • TF = (9/5)TC + 32 • TK = TC + 273.15

  15. Absolute Temperature • Does a sample at 100 C have twice the internal KE as an identical one at 50 C? • Only absolute temperature (eg. Kelvin) is directly proportional to average internal kinetic energy. 100 C 50 C vs.

  16. Types of Thermometers • Mercury- or alcohol-based thermometer • Bi-metal thermometer • Thermocouple • Resistance thermometer • Infrared thermometer • Liquid crystal thermometer

  17. Types of Thermometers

  18. Internal Energy • The total kinetic and potential energy of all the particles in a substance. • Kinetic • Translational • Vibrational • Rotational • Potential • Intermolecular forces

  19. Summary • Temperature • Thermal Energy • Thermal Equilibrium • Measuring Temperature • Temperature scales • Absolute temperature • Thermometers • Internal Energy

  20. Homework • In Tsokos: • Ch. 3.1#2, 3, 4, 5, 6 • Ch. 3.2 #2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 19

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