AP Physics Notes

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AP Physics Notes

• Thermal Physics

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• Derive and Equation to
• Convert from Fahrenheit to Celsius
• Note the freezing and boiling points of water.
• Compare the differences in temperature change on
  the two scales.
• Note the difference in starting points on these
  different scales.

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• Temperature - A measure of the average kinetic
  energy of the particles in a substance
• Measuring Temperature Kelvin, Celsius,
  Fahrenheit
• Conversions
• TF 9/5 TC 32.0
• TK TC 273.15
• Absolute zero - the theoretical temperature at
  which all molecular motion (KE) ceases.

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• Celsius Fahrenheit Kelvin
• Boiling point
• of water 100 212 373
• Freezing point
• of water 0 32 273
• Absolute Zero -273 -459 0

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• Thermal expansion - Increasing the temperature
  causes an unrestricted body to expand
• DL aL0 DT
• - coefficient of linear expansion
• DV bV0 DT
• (not on ref table)
• - coefficient of volumetric expansion
• (see Table 12-1, page 365)
• Water the rare exception

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• Heat (Q) - the process by which energy is
  exchanged between objects because of a difference
  in their temperatures
• Units Joules, Calories, BTU
• 1 calorie 4.186 J or 1 Calorie 1 kcal
  4,186 J
• Internal Energy or Thermal Energy (U) how does
  this differ from temperature and heat?
• Mechanical Equivalent of Heat
• Conservation of Energy
• DPE DKE DU 0

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• Heat (Q) can change temperature
• Q c mDT
• c - Specific Heat Capacity - the quantity of
  energy needed to raise the temperature of 1 kg of
  a substance by 1 degree C at constant pressure
• (see Table 12-2, page 373)

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• Heat (Q) can change phase
• Latent Heat - the energy per unit mass that is
  transferred during a phase change of a substance
• Q m x L
• (see Table 12-3, page378)
• Heat of Fusion (Lf) - the energy per unit mass
  transferred in order to change a substance from
  solid to liquid or from liquid to solid at
  constant temperature and pressure (_at_ MP)
• Heat of Vaporization (Lv) - the energy per unit
  mass transferred in order to change a substance
  from vapor to liquid or from liquid to vapor at
  constant temperature and pressure (_at_ BP)

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• Graph of Temp vs Heat

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• Calorimeter - Device use to experimentally
  determine the specific heat of a substance
  through the process of calorimetry
• The heat lost by the substance is gained by the
  calorimeter (water)
• Qsubstance Qwater

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• Thermal equilibrium - The state in which a system
  in physical contact reaches a constant
  temperature

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• Methods of Transferring Heat
• 3 Types
• 1. Conduction - the transfer of heat through the
  direct contact. Direct molecular collisions
  transfer energy.
• H kA DT
• L
• k thermal conductivity (J/s)
• (see Table 13-1, page 400)
• examples

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• Methods of Transferring Heat (cont)
• 2. Convection - the process in which heat is
  carried from place to place by the bulk movement
  of a fluid
• examples
• Force vs Natural

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• Methods of Transferring Heat (cont)
• Radiation - the process in which energy is
  transferred by means of electromagnetic waves
• Stefan-Boltzmann equation (not on ref table)
• DQ esAT4
• Dt
• s - Stefan-Boltzmann constant
• s 5.67 x 108 W/m2 K4
• e emissivity between 0 and 1
• examples

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• Ideal Gas Law
• PV nRT
• R Universal Gas Constant 8.315 J/(mol K)
• n (mol) mass (g) / molecular mass (g/mol)
• Avogadros Number number of molecules per mole
• NA 6.02 x 1023
• PV NkT
• k Boltzmanns Constant
• k R 8.315 J/(mol K) 1.38 10-23 J/K
• NA 6.02 x 1023/mole

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• Internal Energy for an Ideal Gas
• U N(1/2mv2)
• U 3/2 NkT
• U 3/2 nRT

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• Boyles Law the volume of a gas is inversely
  proportional to the pressure applied to it when
  the temperature is kept constant
• V a 1
• P
• Charless Law the volume of a given amount of
  gas is directly proportional to the absolute
  temperature when the pressure is kept constant
• V a T
• -absolute zero

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• First Law of Thermodynamics
• (Law of Conservation of Energy) - Energy may
  change form but it is neither created or
  destroyed
• DU Q - W
• Special Cases of the 1st Law
• Adiabatic - No Energy Transferred by Heat
• Q 0 DU - W
• Isovolumetric (Isochoric) - Constant Volume
• W 0 DU Q
• Isothermal - Constant Temperature
• DU 0 Q W
• Isobaric - Constant Pressure

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• Second Law of Thermodynamics
• Heat flows naturally from a hot object to a cold
  object heat will not flow spontaneously from a
  cold object to a hot object.
• Application No machine can be made that only
  absorbs energy by heat and then entirely
  transfers the energy out of the engine by an
  equal amount of work.

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• The Efficiency of a Heat Engine
• eff Wnet
• Qh
• eff Qh - QL
• Qh
• eff 1 - QL
• Qh

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• Carnot Efficiency of a Heat Engine
• eff 1- TL
• TH

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• Entropy - The measure of disorder in a system
• DS Q
• t
• The entropy of the universe increases in all
  natural processes.
• Entropy is the driving force behind the 2nd law
  of thermodynamics. Heat spontaneously flows from
  all systems resulting in less than 100
  efficiency.