Physics 213: Unit 2

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Physics 213 Unit 2

• Temperature, Heat, and the Zeroth Law of
  Thermodynamics

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Thermodynamics

• Thermodynamics deals with an internal energy of
  the systems, the thermal energy, and is governed
  by the Laws of Thermodynamics

Thermal Temperature
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Zeroth Law of Thermodynamics

• Temperature in daily life

HOT
WARM
COOL
COLD
What is the definition of temperature ? How to
measure the temperature?
0th Law
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0th Law of Thermodynamics

• If body A and B are each in thermal equilibrium
  with a third body T, then they are in thermal
  equilibrium with each other.

Thermal equilibrium two objects in thermal
contact cease to have any exchange of heat.
Thermal contact Heat can be exchanged.
Heat energy exchanged between objects due to
their temperature difference.
Temperature two objects in thermal equilibrium
with each other are at the same temperature
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Measuring Temperature

• Bring a thermometer to a thermal equilibrium with
  the object

• Thermometer physical property changes with
  temperature
• pressure of gas at constant volume
• length of solid
• Electric resistance
• Volume of liquid

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Temperature Scales

• DEFINE

Freezing temperature of water 0C
Boiling temperature of water 100C
Celsius scale
Different gases all extrapolate to zero
pressure at -273C Kelvin scale
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Temperature Scales

• Kelvin scale T 0 K for P 0 point
• Celsius scale Tc T - 273.15
• Fahrenheit scale TF 9/5 Tc 32
• Thermodynamic scale triple point of water
• T3 273.16 K

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Thermal Expansion

• When heated, objects expand.

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Unusual Behavior of Water

• The maximum density occurs at 4 C
• Above 4 C, expands when heated
• until 100 C
• Below 4 C, expands when cooled
• until 0 C.

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Temperature and Heat

• Internal energy the energy of a system when it
  is stationary - nuclear, chemical, strain, etc.

Thermal energy the energy that changes when the
temperature changes, associated with motions of
atoms, molecules, etc.
Heat Q the transferred energy.
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Units of Heat

• Calorie amount of heat to heat 1 g of water from
  14.5 to 15.5 C

BTU amount of heat to heat 1 lb of water from 63
to 64 F
SI Joule (the same as energy)
1 cal 4.186 J
Joules experiment
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HRW 2E (5th ed.). Suppose the temperature of a
gas at the boiling point of water is 373.15 K.
What then is the limiting value of the ratio of
the pressure of the gas at that boiling point to
its pressure at the triple point of water?
(Assume the volume of the gas is the same at both
temperatures.)
Constant-volume gas thermometer P-T curve
extrapolates to origin.
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HRW 9E (5th ed.). At what temperature do the
following pairs of scales read the same (a)
Fahrenheit and Celsius, (b) Fahrenheit and
Kelvin, and (c) Celsius and Kelvin?
(c) Since TC T - 273.15 the Kelvin and
Celsius temperatures can never have the same
numerical value.
(a) TF (9/5)TC 32 For TF (9/5)TF
32 we get TF -40 F
(b) TF (9/5)TC 32 (9/5)(T - 273.15)
32 For TF (9/5) (TF - 273.15) 32 we get
TF 575 F
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HRW 28P (5th ed.). At 20C, a rod is exactly
20.05 cm long on a steel ruler. Both the rod and
the ruler are placed in an oven at 270C, where
the rod now measures 20.11 cm on the same ruler.
What is the coefficient of thermal expansion for
the material of which the rod is made of?
The change in length for the rod is
20.11cm-20.05cm plus the expansion of the steel
ruler at its 20.11cm mark
?Ls Lsas?T (20.11 cm)(11 x 10-6
/C)(270C-20C) 0.055 cm
?L (20.11cm-20.05cm) 0.055 cm 0.115 cm
The coefficient of thermal expansion of the
material the rod is made of is a ?L/L?T23
x 10-6 /C