# Thermal Physics - PowerPoint PPT Presentation

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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

Lesson 3A

Basic Thermal Concepts

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### Temperature

• The degree of “hotness” of a substance.

• Indicates the direction of flow of “hotness”.

“Hotness” flows from HOT to COLD

HOT

COLD

### 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!

### 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

• 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

• Conduction

• Collisions between atomsor molecules.

• Convection

• Bulk movement of matterfrom one place to another.

• Transmission of energyin the form of light.

### Thermal Equilibrium

• Consider bodies brought into thermal contact:

• Eventually, a steady state is reached:

HOT

HOT

COLD

COLD

WARM

WARM

### 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

• Cooling of a cup of tea

• Thawing food in water

• Getting into a cold bed

• CSI - time of death

• . . .

• Using a thermometer!

### 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 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

• 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

• 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

• Mercury- or alcohol-based thermometer

• Bi-metal thermometer

• Thermocouple

• Resistance thermometer

• Infrared thermometer

• Liquid crystal thermometer

### Internal Energy

• The total kinetic and potential energy of all the particles in a substance.

• Kinetic

• Translational

• Vibrational

• Rotational

• Potential

• Intermolecular forces

### Summary

• Temperature

• Thermal Energy

• Thermal Equilibrium

• Measuring Temperature

• Temperature scales

• Absolute temperature

• Thermometers

• Internal Energy

### 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