Thermodynamics

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Thermodynamics(Study of Heat )
Dr. Shaun Wyngaardt (Room 511)
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Other members of the PHY1024F Team
Course Convenor Dr. Azwinndini Muronga (rm 406)
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Other members of the PHY1024F Team
Course Tutor ???
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Other members of the PHY1024F Team
Lab Coordinators Drs. Rudolph Nchodu (rm. 504)
Shaun Wyngaardt (511)
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Web Information

• Course content can be found at
• http//www.phy.uct.ac.za/courses/phy1024f

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Consultation Times

• Dr Wyngaardt (Tuesdays Thursdays)
• 1300-1400 room 511.
• Course Tutor ???

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Skill which you with Master

• Construction of scientific models
• Develop problem solving techniques
• Develop the ability to perform experiments, do
  measurements, and interpret the data.

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Scientific Terminology
The Moon is made of Cheese

• Scientific Statement
• Scientific Facts
• Scientific Theories/Models
• Scientific Law

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Physical Systems

• An isolated part of the universe which is being
  investigated.
• Why do we isolate things in science?

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ThermoDynamics
Temperature/Heat
Movement/Change
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Outline

• Week 1
• Temperature, Thermal expansion, Heat transfer,
  Zeroth Law of thermodynamics
• Week 2
• Thermal processes (1st law of TD).
• The Kinetic theory of gasses
• Week 3
• The 2nd Law of Thermodynamics the Physics
  behind Heat engines.

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Thermodynamic system

• Thermodynamic systems are
• Macroscopic (size of everyday things)
• Homogeneous (same composition and structure
  throughout material)
• Isotropic (identical physical properties in all
  directions)
• Uncharged (no net electric charge)
• Chemically inert (no chemical processes)
• Experiences no change in its total mechanical
  energy (no stress or strain on the system).

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Thermal properties of a system

• What is temperature?
• Macroscopic description
• a measure of the hotness/coldness of a body

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• In Physics we distinguish between temperature and
  heat.
• Heat is defined as the transfer (donation) of
  internal energy between different objects (in
  contact with each other) at different
  temperatures (Objects in thermal contact).
• Heat transfer -gt state of thermal equilibrium
  (same temperature).

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Zeroth Law of thermodynamics

• If systems A and B are in thermal equilibrium
  with system C then A and B are in thermal
  equilibrium with each other.

A
C
B
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Zeroth Law of thermodynamics

• If system A and B are in thermal equilibrium with
  system C then A and B are in thermal equilibrium
  with each other.

A
B
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Measures of temperature and heat

• Heat Energy transferred Joule
• Other units of heat energy include Calories (cal)
  

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• Is the human body a good thermometer?
• Most materials respond to temperature changes by
  expanding when heated or contracting when cooled.

http//home.howstuffworks.com/therm1.htm
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Temperature scales

• Two commonly used temperature scales
• Fahrenheit scale - Daniel Fahrenheit arbitrarily
  decided that the freezing and boiling points of
  water would be separated by 180 degrees, and he
  pegged freezing water at 32 degrees. So he made a
  thermometer, stuck it in freezing water and
  marked the level of the mercury on the glass as
  32 degrees. Then he stuck the same thermometer in
  boiling water and marked the level of the mercury
  as 212 degrees. He then put 180 evenly spaced
  marks between those two points.
• Celsius scale - Anders Celsius arbitrarily
  decided that the freezing and boiling points of
  water would be separated by 100 degrees, and he
  pegged the freezing point of water at 100
  degrees. (His scale was later inverted, so the
  boiling point of water became 100 degrees and the
  freezing point became 0 degrees.)

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Absolute zero temperature

• When a gas is cooled its pressure drops.
• Gasses which are not near its liquefaction
  temperature follow a linear temperature pressure
  relationship of the form

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Temperature in degrees Celsius
Pressure
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Kelvin scale
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Classroom Exercise

• Like the Kelvin scale, the Rankine scale is an
  absolute temperature scale absolute is zero
  degrees Rankine (0oR). However, the units of this
  scale are the same are the size as those on the
  Fahrenheit scale rather than the celcius scale.
  What is the numerical value of the triple point
  of water (25oC) on the Rankine scale.

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K
oC
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Thermal properties of Macroscopic Objects
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Thermal expansion in solids and liquids

• Most objects expand when heated.
• This expansion need to be considered in various
  engineering and architectural structures such as
  railway lines, windows pains, etc.
• Amount of thermal expansion depends on the
  material which is heated.

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• Quantifying thermal expansion experimental we
  find that

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• Quantifying thermal expansion experimental we
  find that

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• Quantifying thermal expansion experimental we
  find that

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• Thermal expansion depends on the initial length
  of the rod.

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• Thermal expansion depends on the initial length
  of the temperature change.

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• Hence the linear thermal expansion of a rod is
  given by

Expansion coefficient
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Thermal expansion of an area
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Thermal expansion of an area
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Thermal expansion of a volume
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Coefficients of thermal expansion

• http//hypertextbook.com/physics/thermal/expansion

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Thermal expansion in kettles
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Exercise 1

• A surveyor uses a steel measuring tape that is
  exactly 50.0 km long at a temperature of 20
  degrees C. What is its length on a hot summer day
  when the temperature is 35 degrees C?

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Exercise 2

• A glass flask with a volume 200 cm3 is filled to
  the brim with mercury at 20 oC. How much mercury
  overflows when the temperature of the system is
  raised to 100 oC? The coefficient of linear
  expansion of the glass is 0.4 X 10-5 K-1, while
  the volume expansion of mercury is 18 X 10-5 K-1.

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Calorimetry

• When heat is transferred two things could happen
• Temperature could change
• System could undergo a phase change (melting
  ice).
• Convention Heat transfer to a system is while
  heat transfer from a system is -

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Case 1 Temperature change
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Case 1 Temperature change
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Case 1 Temperature change
specific heat capacity
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Case 1 Temperature change
of moles
Molecular mass
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Case 1 Temperature change
Molar specific heat capacity
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Phase change

• Solid lt-gtLiquidlt-gtGaslt-gtPlasma
• The temperature of a system undergoing a phase
  change remain the same.
• The amount of heat energy required for a phase
  change depend on the amount (mass) of the
  substance we have.

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Phase change

• Hence

Latent heat
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Processes of heat transfer

• There are 3 way to transfer heat
• Conduction
• Convection
• Radiation

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Heat Conduction
Heat energy moves
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Heat Conduction
Heat energy moves
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Heat Conduction
Heat energy moves
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Heat Conduction
Heat energy moves
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Heat Convection

• The transfer of heat by means of the mass
  movement of molecules from one place to another.

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Heat Convection
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Heat Convection
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Radiation of Heat Energy

• Both the transfer of heat through conduction and
  convection require the present of matter.
• How does heat energy move through empty space
  from the hot sun to earth?

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Radiation of Heat Energy

• All hot objects above absolute zero (0K) emit
  ELECTROMAGNETIC RADIATION in one form or another
  (microwaves, radiowaves, light, x-rays).
• The rate of radiation is given by the
  Stephan-Boltzmann equation

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Radiation of Heat Energy

• Stephan-Boltzmann equation

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Radiation of Heat Energy
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Radiation of Heat Energy

• Radiation correction due to the colour of the
  radiating object.

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Radiation of Heat Energy

• Radiation can be absorbed from the environment
  surrounding an object, thus increasing its
  temperature.
• At the same time the object could emit radiation
  to its surroundings

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Thermal effects in an Ideal gas

• Robert Boyle 1660 (Gas consists of particles)

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Thermal effects in an Ideal gas

• Robert Boyle 1660
• At constant temperature he observed that

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• Furthermore this constant depends linearly on the
  temperature

• The value of PV also depends on the amount of gas
  particles in the container.

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• Avogadros number of particles (atoms/molecules)

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Idea Gas Relationships
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Exercise 3

• When excessive heat is produced within the body,
  it must be transferred to the skin and dispersed
  if the body interior is to be maintained at the
  normal value of 37.0 degrees Celsius. One
  possible mechanism for transfer is conduction
  through body fat. Suppose that heat travels
  through 0.030 m of fat in reaching the skin,
  which has a total surface area of 1.7 m2 and a
  temperature of 34.0 degrees Celsius. Find the
  amount of heat that reaches the skin in half an
  hour (1800 s) K(Fat) 0.2 J/(s.moC).

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Thermal Processes and the 1st Law of
Thermodynamics

• We reap the practical benefits of thermodynamic
  processes on a daily basis.
• Examples include driving cars, turning on an air
  conditioner, cooking a meal,
• Central to all processes in the Conservation of
  Energy (energy transforms from one form to
  another)

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Thermal Processes

• Four main thermodynamic quantities to play around
  with (Temperature, Pressure, Volume, and Heat).
• Thermal processes are characterised by keeping
  one of these 4 quantities fixed.

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Thermal Processes

• Four thermodynamic processes include
• Isothermal process Temperature of system is
  fixed.
• Isobaric process Pressure is fixed.
• Isochoric process Volume is fixed.
• Adiabatic process hardly no heat is transfer to
  or from the system (Thermus flask).

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Thermal systems have Internal Energy
Particles inside container have internal kinetic
energy
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1st law of Thermodynamics

• We can change the internal energy by
• doing work on it or
• heating it.
• Conversion Work done on the system is and work
  done by the system is -.

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1st law of Thermodynamics
Change in internal energy
Heat applied to the system
Work done by the system on surroundings
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Work done by system on surroundings
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Work done by gas in Isobaric process
P Constant
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Work done by gas in Isochoric process
V Constant
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Work done by gas in Isothermal process
T Constant