Thermal physics
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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

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Thermal physics

Thermal Physics

Lesson 3A

Basic Thermal Concepts


Thermal physics

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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 temperature

Measuring Temperature


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


Types of thermometers1

Types of Thermometers


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


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