Temperature Temperature Microscopic Atoms  Atoms in matter are in

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Temperature Temperature Microscopic Atoms  Atoms in matter are in Powered By Docstoc
Microscopic Atoms
   Atoms in matter are in constant motion.
   Interaction of atoms determines the state of matter.

   Solid                  Liquid               Gas
     • Atoms vibrate         • Atoms close,       • Atoms apart,
       in a nearly             but free to          freely moving in
       fixed position          move around          the volume
Macroscopic Properties
   There are about 5 x 1024
                                   Microscopic properties:
    atoms in a golf ball.
   We track its motion as a       mass, position, velocity, energy
    whole, not as atoms.

   Density and pressure apply
                                   Macroscopic properties:
    to the whole object, not the
    atoms.                         mass, position, velocity, energy
   These are macroscopic          and
                                   density, pressure, temperature
Hot and Cold
   Temperature is a
    macroscopic property of
    • Based on statistics
    • Doesn’t generally apply to
      single atoms

   Hot matter has more energy
    per atom on average than
    cold matter.
    • Single atoms may have less
      energy in a hot item
Thermal Contact
heater               Two cups of water are in
                       • Heat one cup
                       • Compare macroscopic

                     If they are the same they are
heater                in thermal contact.
                       • eg. metal cups

                     If different they are insulated.
Thermal Equilibrium
   Two systems have the same temperature if they are
    in thermal equilibrium.
    • Equilibrium between systems
    • Measure of macroscopic properties
   If two systems are not in thermodynamic equilibrium,
    they are not in thermal contact.
Law Zero
   If two systems are each in thermodynamic
    equilibrium with a third system, then they are in
    thermodynamic equilibrium with each other.

   This is the Zeroth Law of Thermodynamics.

                            A is in thermal equilibrium with B.
      A      B       C      C is in thermal equilibrium with B.
                            Therefore, A is in thermal
                            equilibrium with C.
Gas Thermometer
   A system with known macroscopic properties may be
    placed in thermodynamic equilibrium.
   A device that uses this is a thermometer.

                             This thermometer uses the
                             pressure of gas in a bulb.

                             The meter measures the height
                             in a manometer or barometer.
   Temperature requires a          10-4 K   Superfluid liquid helium
    scale to compare different      4K       Helium boils
    systems.                        77 K     Air boils
   The Kelvin (K) is the SI unit   273 K    Water melts
    of temperature.
                                    373 K    Water boils
     • Based on behavior of water
     • Linear pressure scale
                                    630 K    Mercury boils
     • Not degrees Kelvin           1000 K   Copper melts
                                    6000 K   Surface of the sun
                        P           106 K    Solar corona
          T  273 .16
                        P3          108 K    Hydrogen bomb
Temperature Scales
   For everyday temperatures      The English system uses the
    the Celsius scale (C) is       Fahrenheit scale (F).
                                   Ice point at 1 atm is 32.
   Each C is the same            Boiling point at 1 atm is
    magnitude as 1 K.               212.
    • The zero is different        Each F is 5/9 of a C.
    • 0 C = 273.15 K
    • Not quite T at P3
                                       TF  TC  32
Body Temperature
   Normal body temperature is         The general formula applies
    98.6 F. What is the                for a conversion between
    equivalent in C and K?             scales.
                                        • TC = (5/9)(TF – 32)
   If your fever is 101.6 F, by       • (5/9)(98.6 – 32.0) = 37.0 C
    how much has it risen in C         • T = TC + 273.15 = 310.2 K
    and K?
                                       The difference use the
                                        fractional change.
                                        • DTC = (5/9) DTF
                                        • (5/9)(101.6 – 98.6) = 1.7 C
                                        • DT = DTC = 1.7 K


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