Thermal Physics
Chapter 10
Temperature and
Heat
•
Temperature
•
Thermometers
•
Thermal Expansion
•
Ideal Gas Law
•
Kinetic Theory of
Gases
Temperature
•
Temperature is a measure of the “Hotness” or
“Coldness” of an object.
•
Temperature is measured by devices called
thermometers: there are many different types used
depending on the temperature range being measured.
Thermal Equilibrium
•
Objects in “thermal contact” can exchange heat energy.
•
Heat energy flows from hot (higher temperature) to cold
(lower temperature).
•
When two objects have the same temperature, there is
no net flow of heat energy, and the objects are said to be
in “thermal equilibrium”.
Zeroth Law of
Thermodynamics
•
If two objects A and B are in thermal equilibrium with a
third object, C, they are in thermal equilibrium with
each other.
•
Translation: If A and C have the same temperature, and
B and C have the same temperature, then A and B have
the same temperature. (Think A=C and B=C, so A=B.)
Mercury
Thermometers
•
When heat energy is added to
a system and its temperature
rises, the mercury inside the
thermometer expands to a
higher level.
•Daniel Gabriel Fahrenheit
(1686-1736) was the German
physicist who invented the
alcohol thermometer in 1709,
and the mercury thermometer
in 1714. In 1724, he
introduced the temperature
scale that bears his name Fahrenheit Scale.
Constant Volume
Thermometer
•
In a constant volume thermometer,
the gas volume is held constant
and the gas pressure is measured.
•
The temperature varies in direct
proportion to the pressure.
Kelvin’s Experiments
•Lord William Thomson Kelvin performed
a series of experiments using the constant
volume gas thermometer.
•He discovered that different gases and
different amounts of gas all tended toward
zero volume at -273 °C. He called this
temperature absolute zero, the coldest
possible temperature.
•In 1848 he proposed a temperature scale
based on the Celsius scale, but starting
with zero degrees at absolute zero.
•This temperature scale is called the
absolute or Kelvin scale.
Kelvin Temperatures
•
The Kelvin temperature scale is
used in physics and chemistry
formulas.
•
The Kelvin temperature is a
measure of how much thermal
energy (kinetic energy of random
motion) is contained in a
substance.
Common
Temperature Scales
•
These linear thermometers
are calibrated by defining
the temperature scale at
two points: the ice point
and the steam point of
water.
•
Kelvins = °C + 273.15
°C = Kelvins - 273.15
•
°C = (5/9)(°F-32)
°F = (9/5)°C + 32
Thermal Expansion
•
Almost all materials
expand when they
are heated and
grow smaller when
cooled.
•
These train tracks
were laid in cool
weather. When the
weather got warmer
in the summer...
Expansion Joints
•
To prevent concrete
bridges in roads from
breaking when
expanding or
shrinking, they are
built with expansion
joints.
•
Modern railroad also
have expansion joints.
More Expansion
Joints
•
This wall is built with a straight line joint which is filled
with a flexible material.
•
Concrete and asphalt roads are also built this way.
Coefficients of
Expansion
Linear Expansion
Volume Expansion