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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

Thermal Physics

Lesson 3A

Basic Thermal Concepts

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temperature
Temperature
  • The degree of “hotness” of a substance.
  • Indicates the direction of flow of “hotness”.

“Hotness” flows from HOT to COLD

HOT

COLD

temperature1
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!

temperature2
Temperature
  • The higher the temperature, the higher the average speed of the particles.

N.B.Particles don’t all have the same speed!

thermal energy
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
modes of heat transfer
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.
thermal equilibrium
Thermal Equilibrium
  • Consider bodies brought into thermal contact:
  • Eventually, a steady state is reached:

HOT

HOT

COLD

COLD

WARM

WARM

thermal equilibrium1
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

examples of thermal equilibrium
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!
measuring temperature1
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

measuring temperature2
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)
temperature scales
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
absolute temperature
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.

types of thermometers
Types of Thermometers
  • Mercury- or alcohol-based thermometer
  • Bi-metal thermometer
  • Thermocouple
  • Resistance thermometer
  • Infrared thermometer
  • Liquid crystal thermometer
internal energy
Internal Energy
  • The total kinetic and potential energy of all the particles in a substance.
  • Kinetic
    • Translational
    • Vibrational
    • Rotational
  • Potential
    • Intermolecular forces
summary
Summary
  • Temperature
  • Thermal Energy
  • Thermal Equilibrium
  • Measuring Temperature
    • Temperature scales
    • Absolute temperature
    • Thermometers
  • Internal Energy
homework
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
ad