CONCEPTUAL MATERIAL FOR TEST ONE - Chapters 12-15
CHAPTER 12: Thermal Properties of Matter
Ideal gas
- a model of a gas where the molecules have zero size and are
perfectly elastic
Absolute zero
- the temperature at which the pressure of an ideal gas is zero
- the point at which, in classical physics, all thermal motion ceases
Absolute temperature scale
- a temperature scale proportional to the pressure of an ideal gas
kept at constant volume
Temperature
- the effect of the random kinetic energy of atoms and molecules
- proportional to the average kinetic energy per molecule
Celsius
- essentially defined between the freezing (0 C) and boiling (100 C)
points of water at one atmosphere pressure
Kelvin
- degree steps the same as celsius, measured from absolute zero
Thermal expansion
- occurs when atoms vibrate more vigorously with increasing temper-
ature, forcing neighboring atoms away, increasing the substance's
volume
Know the ideal gas law and recall that P is absolute pressure and T
is absolute temperature in this law.
CHAPTER 13: Heat and Thermal Energy
Thermal energy
- the disordered (random) KE of a group of atoms
- NOT the same as heat
Heat
- is the transfer of energy by temperature differences only
Calorie
- the amount of heat needed to raise 1 gram of water from 14.5 C to
15.5 C (but used over the entire temperature range of liquid water)
Mechanical equivalent of heat
- asserts that heat is a form of energy, in particular...
- asserts that mechanical energy can be converted to heat energy
Thermal equilibrium
- exists for two bodies when no heat flows between them
Zeroth law of thermodynamics
- bodies in thermal equilibrium are at the same temperature
Specific heat
- is different for different substances
- the heat flow necessary to change the temperature of a unit mass of
a substance by one unit of temperature
- by definition of the calorie (above) the specific heat of water is
one calorie per gram per degree celsius
Heat of fusion
- the amount of heat needed to change a unit mass of a substance from
a solid to a liquid = the amount of heat given up by a unit mass of
liquid when changing to a solid (SAME TEMPERATURE BEFORE AND AFTER)
- the energy needed to overcome the potential energy involved in the
attraction of the atoms or molecules forming the solid
- the change of phase ("change of state" in your text) does not have
to occur at melting (e.g., the sublimation of snow)
Heat of vaporization
- the amount of heat needed to change a unit mass of a substance from
a liquid to a gas = the amount of heat given up by a unit mass of
gas when changing to a liquid (SAME TEMPERATURE BEFORE AND AFTER)
- the energy needed to overcome the potential energy involved in the
attraction of the atoms or molecules forming the liquid, in
particular to overcome the surface tension of the liquid
- the change of phase does not have to occur at boiling (e.g., the
evaporation of water from a pan)
Conservation of energy in phase change
- heats of fusion and vaporization do not depend on which direction
the phase change occurs
Vapor pressure
- the contribution to pressure due to that part of a gas considered
to be "vapor" (e.g., water vapor in air)
Saturation vapor pressure
- when the vapor pressure reaches the point where as much vapor is
entering the liquid as leaving it
Boiling
- occurs when the saturation vapor pressure of the liquid equals that
of the ambient pressure (one atmosphere at sea level, lower at
higher altitudes, higher in a pressure cooker)
- occurs at the boiling point temperature: increase in heating only
leads to more rapid boiling, not a higher temperature
Thermal radiation
- the emission of electromagnetic radiation due to thermal motion
- can be of any wavelength, but most of the thermal radiation emitted
at "room temperature" is in the infrared
- intensity ("brightness") depends on the FOURTH POWER (!) of the
absolute temperature
- heat is transferred from a hotter to a cooler body: the hotter
body is a net emitter of radiation and the cooler body a net
absorber
Convection
- heat transfer by mass movement of fluids
Free convection
- driven by gravity (buoyancy): warmer fluid is less dense than
colder (usually) and tends to rise while colder fluid tends to sink
Forced convection
- driven by a fan, for example
Conduction
- heat flow due to contact between two objects
- hotter, faster moving atoms impart energy to cooler, slower moving
atoms through collisions
Thermal conductivity
- different substances have different thermal conductivities
- the larger the thermal conductivity, the better the substance
conducts heat
CHAPTER 14: Thermodynamics
First law of thermodynamics
- same as the conservation of energy where heat is included as a form
of energy that can be converted from and to other forms
Internal energy
- the disordered energy contained by a body (can be kinetic,
potential, and other forms)
- by the first law of thermodynamices, it equals the heat added to a
substance plus the (randomizing) work done on it
State
- a set of quantities that specifies a system (e.g., P,V,T for ideal
gas system), called "state variables"
- not defined for a system if any state variables is not well defined
(for example, if the temperature varies in the gas from one place to
another)
Equation of state
- an equation in which the state variables are related to one
another (e.g., PV = nRT for ideal gas)
Process
- occurs when a system changes from one state to another
- isothermal: constant temperature process
- isobaric: constant pressure process
- isovolumic: process in which the volume is constant
Thermodynamic equilibrium
- occurs when there is thermal, mechanical, and chemical equilibrium
- a process has to take the system out of thermodynamic equilibrium
to change its state, although this can be done slowly enough that
the system remains approximately in equilibrium
Thermodynamic work
- performed by changing the volume of the system
- equal to the area "under the curve" on a PV-diagram
Engine
- converts energy into work
Heat engine
- converts heat energy into work
- works between high and low temperature reservoirs of heat
Thermodynamic cycle
- a series of processes on a system that returns the system to its
original state; depicted on a PV-diagram as a closed curve
Entropy and the second law of thermodynamics
- a mathematical measure of the amount of disorder in a system
- must always either increase or stay the same for an isolated system
- disorder in an isolated system can at best remain constant
- interacting systems can decrease their disorder by exporting disorder
to other systems (water freezes to crystalline ice and releases
disorder as heat)
Chapter 15 - Electrostatics - Forces
Electric charge
- two types: positive and negative
- like charges repel, opposites attract
- quantized in units of the magnitude of charge on an electron
- SI unit = coulomb (C) = charge carried by a current of one
ampere (A) in one second's time
- conserved: charge (net charge) can neither be created nor
destroyed
- electron affinity: a quantum effect whereby some substances hold
onto electrons more tenaciously than others
- conductors: substances in which there exists a relatively large
number of charge carriers (charged particles that can move around
rather freely - usually electrons, as in metals)
. any excess charge present is found on their outer surfaces
- insulators: substances that have few electrons (or other charge
carriers) free to move around
- dielectrics
. insulators
. can be polarized (separation of positive and negative charges)
. polarization results in positive and negative surface charge
densities
Electrostatic Force
- Coulomb's law (Coulomb force)
. mathematically similar to Newton's gravitational force, except
can be attractive or repulsive
. directly proportional to the product of the magnitude of the
charges
. inversely proportional to the square of the separation between
the charges (inverse square-law force)
. for the amount of matter involved, much larger than gravity
. like all forces: a vector quantity
Electric (actually "Electrostatic") Field
- Vector field
. magnitude = magnitude of the Coulomb force on a unit charge
. direction = direction of the Coulomb force on a positive charge
. superposition: electric fields at a given point in space due to
different charges/charge distributions add like vectors to give
the total electric field
- Important special electric fields
. due to point charge: falls off as one over the distance squared
. electric field outside spherical distribution of charge is like
that of a point charge located at the center of the distribution
with a charge equal to the total charge in the distribution
. uniform electric field: magnitude and direction of electric
field the same over the region where the field exists
. approximate uniform field found between sufficiently close,
oppositely charged metal plates (parallel-plate capacitor)
- Electric field lines
. pictures only; do not exist in reality
. drawn to indicate direction of electric field
. originate on positive charge and terminate on negative charge
. never cross (because the electric field can't point two ways at
the same point in space)
. always perpendicular to the surface of a conductor
- Dipole
. formed by two equal and opposite point charges
. electric field of dipole diminishes with distance more rapidly
than that of single charge