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Thermal Physics Temperature Thermometers Thermal Expansion.

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Thermal Physics Temperature Thermometers Thermal Expansion
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Page 1: Thermal Physics Temperature Thermometers Thermal Expansion.

Thermal Physics

Temperature

Thermometers

Thermal Expansion

Page 2: Thermal Physics Temperature Thermometers Thermal Expansion.

Definitions

• Thermal Contact – if energy can be exchanged between two objects, then they are in thermal contact

• Thermal Equilibrium – if two objects are in thermal contact and there is no exchange of energy, then they are in thermal equilibrium

Page 3: Thermal Physics Temperature Thermometers Thermal Expansion.

The Law of Equilibrium

• Zeroth Law of Thermodynamics– If objects A and B are separately in thermal

equilibrium with object C, then A and B are in thermal equilibrium with each other

Definition of Temperature

• If objects A and B are in thermal equilibrium, then they are at the same temperature.

Page 4: Thermal Physics Temperature Thermometers Thermal Expansion.

Constant V Gas Thermometer

Fig. 10.3, p.324

• Reference points– 100°C for boiling water– 0°C for freezing water

• Extrapolate graph to zero pressure to find absolute zero temperature

Fig. 10.5, p.325

Page 5: Thermal Physics Temperature Thermometers Thermal Expansion.

Temperature Scales• Column of fluid

changes height in response to warmth or coolness of surroundings

• Numbers assigned to the height establishes the temperature scale

• Each division in the scale is called a degreeFig. 10.7, p.326

Page 6: Thermal Physics Temperature Thermometers Thermal Expansion.

Temperature Scales• Defined by:

– Height of column when water freezes (0°C = 32°F)– Height of column when water boils (100°C = 212°F)

• Note: −40°C = −40°F

Page 7: Thermal Physics Temperature Thermometers Thermal Expansion.

Conversions

Slope:

Intercept = 32°F

5

9

C100

F180

C0C100

F32F212

C

F

T

T

Page 8: Thermal Physics Temperature Thermometers Thermal Expansion.

Conversions

325

9CF TT 32

9

5FC TT

CF TT 5

9FC TT

9

5

From °C to °F From °F to °C

Temperature Reading

Temperature Change

Page 9: Thermal Physics Temperature Thermometers Thermal Expansion.

Absolute Zero and Kelvin Scale

• Temperature is in units called kelvins (K)• T = 0 K is called absolute zero

• Represents the temperature at which an ideal gas:– Has zero volume (at constant pressure)– Has zero pressure (at constant volume)

K 15.273 CTT CTT

Page 10: Thermal Physics Temperature Thermometers Thermal Expansion.

Thermal Expansion

• For solids and liquids:– Energy increase via heat input– Atoms vibrate with greater amplitude– Average separation increases

• Leads to macroscopic expansionsFig. 9.1, p.269

Fig. 10.8, p.329

Page 11: Thermal Physics Temperature Thermometers Thermal Expansion.

Expansion Coefficients

4.100 TLL

5.100 TAA

6.100 TVV

2 3

Linear Expansion – 1D

Area Expansion – 2D

Volume Expansion – 3D

If is the same in all directions then

Page 12: Thermal Physics Temperature Thermometers Thermal Expansion.

No Life Without Water

Fig. 10.11, p.334As water cools, it first contracts, but

then expands near freezing


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