AP Physics Notes

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AP Physics Notes

• Atomic and Nuclear Physics
• Chapters 29 - 32

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• Does light travel as a wave?
• What evidence do we have?
• Does light travel as a particle?
• What evidence do we have?
• Wave Particle Duality

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29.1 Wave Particle Duality
When a beam of electrons is used in a Youngs
double slit experiment, a fringe pattern occurs,
indicating interference effects.
Waves can exhibit particle-like
characteristics, and particles can exhibit
wave-like characteristics.
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• Blackbody Radiation
• As the temperature increases the electromagnetic
  radiation emitted by bodies is strongest at
  higher frequencies
• http//physics.bu.edu/duffy/semester2/c34_blackbo
  dy.html
• http//phet.colorado.edu/new/simulations/sims.php?
  simBlackbody_Spectrum
• file//bcsdapp/examview/PhET-1.0/new/simulations/
  sims8eab.html?simBlackbody_Spectrum

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29.2 Blackbody Radiation and Plancks Constant
All bodies, no matter how hot or
cold, continuously radiate electromagnetic waves.
Electromagnetic energy is quantized.
frequency
Plancks constant
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• Atomic Theory
• Thomson (1897) - atom is divisible.
• -plum pudding model
• Rutherford (1908) - Atoms had a concentrated
  nucleus
• -gold foil experiment

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• Atomic Theory
• Bohr (1913) - Electrons move in definite orbits
  around the nucleus.
• Each orbital is a different energy level.

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• Bohr developed his model of the atom based on
  spectral emission and absorption patterns.
• http//lectureonline.cl.msu.edu/mmp/kap29/Bohr/ap
  p.htm
• http//home.achilles.net/jtalbot/data/elements/in
  dex.html
• http//phet.colorado.edu/new/simulations/sims.php?
  simModels_of_the_Hydrogen_Atom
• file//bcsdapp/examview/PhET-1.0/new/simulations/
  sims0707.html?simModels_of_the_Hydrogen_Atom
• Study of Spectroscopy (using a spectrometer)
• Quantum - fixed amount
• Photons quantized energy in the form of light
• Review Electronvolt (eV) and Potential
  Difference (V)

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• Plancks Quantum Hypothesis
• Energy distributed among the oscillating
  electric charges of the molecules is not
  continuous, it consisted of finite number of very
  small discrete amounts, related to frequency
• Ephoton hf
• h Plancks Constant 6.63 x 10-34 Js
• or (since c lf) E hc/l
• Characteristic patterns resulted from the
  quantized nature of
• light. Certain wavelengths of light are produced
  as electrons
• change orbitals.
• Ephoton Ei Ef

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30.3 The Bohr Model of the Hydrogen Atom
ENERGY LEVEL DIAGRAMS
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Production of an Emission Spectrum
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Where are the photons for the other electron
transitions?
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• Applications of Spectroscopy
• Light spectra can shift due to the relative
  motion between the observer and the light source
  Doppler Effect

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30.2 Line Spectra
The Line Spectrum of Hydrogen
Lyman series
Balmer series
Paschen series
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30.3 The Bohr Model of the Hydrogen Atom
In the Bohr model, a photon is emitted when the
electron drops from a larger, higher-energy orbit
to a smaller, lower energy orbit.
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• Photoelectric Effect
• When light shines on a metal surface, electrons
  are emitted
• KE hf - hf0
• hf0 work function, energy needed to remove the
  e-
• http//physics.berea.edu/king/Teaching/ModPhys/QM
  /Photoelectric/Photoelectric.html
• http//phet.colorado.edu/new/simulations/sims.php?
  simPhotoelectric_Effect
• file//bcsdapp/examview/PhET-1.0/new/simulations/
  sims1db0.html?simPhotoelectric_Effect
• Energy of the electron based on frequency, not
  the intensity of the light.
• Disproves a classical model.
• Einstein won a Nobel Prize (1921) for this
  theory.
• Based on the work of Planck.
• Tested and proven by Millikan.

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29.3 Photons and the Photoelectric Effect
Experimental evidence that light consists of
photons comes from a phenomenon called the
photoelectric effect.
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29.3 Photons and the Photoelectric Effect
When light shines on a metal, a photon can give
up its energy to an electron in that metal. The
minimum energy required to remove the least
strongly held electrons is called the work
function.
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29.3 Photons and the Photoelectric Effect
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29.3 Photons and the Photoelectric Effect
Example 2 The Photoelectric Effect for a Silver
Surface The work function for a silver surface
is 4.73 eV. Find the minimum frequency that
light must have to eject electrons from the
surface.
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29.3 Photons and the Photoelectric Effect
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29.3 Photons and the Photoelectric Effect
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• Quantum Mechanics the study that unifies the
  wave-particle duality into a consistent theory
• Other Significant Works
• Compton Effect Photon collides with an electron
  and changes l (energy)
• http//www.student.nada.kth.se/f93-jhu/phys_sim/
  compton/Compton.htm

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29.4 The Momentum of a Photon and the Compton
Effect
The scattered photon and the recoil electron
depart the collision in different
directions. Due to conservation of energy, the
scattered photon must have a smaller
frequency. This is called the Compton effect.
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29.4 The Momentum of a Photon and the Compton
Effect
Momentum and energy are conserved in the
collision.
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29.4 The Momentum of a Photon and the Compton
Effect
Conceptual Example 4 Solar Sails and the
Propulsion of Spaceships One propulsion method
that is currently being studied for interstellar
travel uses a large sail. The intent is that
sunlight striking the sail creates a force that
pushes the ship away from the sun, much as
wind propels a sailboat. Does such a design have
any hope of working and, if so, should the
surface facing the sun be shiny like a mirror or
black, in order to produce the greatest force?
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• Broglie Waves all matter has both wave and
  particle properties (l h/p h/mv)

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29.5 The de Broglie Wavelength and the Wave
Nature of Matter
The wavelength of a particle is given by the
same relation that applies to a photon
de Broglie wavelength
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29.5 The de Broglie Wavelength and the Wave
Nature of Matter
Neutron diffraction is a manifestation of the
wave-like properties of particles.
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29.5 The de Broglie Wavelength and the Wave
Nature of Matter
Example 5 The de Broglie Wavelength of an
Electron and a Baseball Determine the de Broglie
wavelength of (a) an electron moving at a speed
of 6.0x106 m/s and (b) a baseball (mass 0.15
kg) moving at a speed of 13 m/s.
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29.5 The de Broglie Wavelength and the Wave
Nature of Matter
Particles are waves of probability.
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• Heisenberg Uncertainty Principle momentum and
  position of an electron cannot be determined
  concurrently

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29.6 The Heisenberg Uncertainty Principle
THE HEISENBERG UNCERTAINTY PRINCIPLE Momentum
and position
Uncertainty in particles position along the y
direction
Uncertainty in y component of the particles
momentum
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29.6 The Heisenberg Uncertainty Principle
THE HEISENBERG UNCERTAINTY PRINCIPLE Energy and
time
time interval during which the particle is in
that state
Uncertainty in the energy of a particle when the
particle is in a certain state
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31.1 Nuclear Structure
The atomic nucleus consists of positively charged
protons and neutral neutrons.
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31.1 Nuclear Structure
atomic mass number
atomic number
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31.1 Nuclear Structure
Nuclei that contain the same number of protons
but a different number of neutrons are known as
isotopes.
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31.1 Nuclear Structure
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31.1 Nuclear Structure
Conceptual Example 1 Nuclear Density It is well
known that lead and oxygen contain different
atoms and that the density of solid lead is much
greater than gaseous oxygen. Using the equation,
decide whether the density of the nucleus in
a lead atom is greater than, approximately equal
to, or less than that in an oxygen atom.
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31.2 The Strong Nuclear Force and the Stability
of the Nucleus
The mutual repulsion of the protons tends to push
the nucleus apart. What then, holds the nucleus
together? The strong nuclear force.
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31.2 The Strong Nuclear Force and the Stability
of the Nucleus
As nuclei get larger, more neutrons are required
for stability. The neutrons act like
glue without adding more repulsive force.
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31.3 The Mass Deficit of the Nucleus and Nuclear
Binding Energy
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31.3 The Mass Deficit of the Nucleus and Nuclear
Binding Energy
Example 3 The Binding Energy of the Helium
Nucleus Revisited The atomic mass of helium is
4.0026u and the atomic mass of hydrogen is
1.0078u. Using atomic mass units, instead of
kilograms, obtain the binding energy of the
helium nucleus.
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31.3 The Mass Deficit of the Nucleus and Nuclear
Binding Energy
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31.3 The Mass Deficit of the Nucleus and Nuclear
Binding Energy
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• Nuclear Physics
• Einstein's famous equation that relates mass to
  energy
• E mc2

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• Compare mass of He to its components

How is this mass accounted for? Binding Energy E
mc2 E 4.53981 x 10-12 J 28.30 MeV (1eV
1.6 x 10-19 J)
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• The 4 Fundamental Forces
• (in order of strength)
• Strong Nuclear Holds nucleus together
• (short range)
• 2. Electromagnetic
• Electrostatic Forces (ie Coulombs Law)
• Magnetic Forces
• 3. Weak Nuclear binds subatomic particles
  (short range)
• 4. Gravity
• (ie Newtons Law of Universal Gravitation)

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• Nuclear Decay Unstable nuclei break down
• 3 Types of Radiation
• Alpha Particles Helium nucleus (2P, 2N)
• Beta Particles Nuclear Electron
• Gamma Ray electromagnetic radiation
• Fission - splits a nucleus
• Fusion - small particle are combined

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31.4 Radioactivity
A magnetic field separates three types of
particles emitted by radioactive nuclei.
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31.4 Radioactivity
a DECAY
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31.4 Radioactivity
A smoke detector
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31.4 Radioactivity
ß DECAY
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31.4 Radioactivity
? DECAY
excited energy state
lower energy state
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31.4 Radioactivity
Gamma knife
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31.5 The Neutrino
During beta decay, energy is released. However,
it is found that most beta particles do not have
enough kinetic energy to account for all of the
energy released. The additional energy is
carried away by a neutrino.
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31.6 Radioactive Decay and Activity
The half-life of a radioactive decay is the time
in which ½ of the radioactive nuclei
disintegrate.
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31.6 Radioactive Decay and Activity
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31.7 Radioactive Dating
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31.7 Radioactive Dating
Conceptual Example 12 Dating a Bottle of Wine A
bottle of red wine is thought to have been sealed
about 5 years ago. The wine contains a number of
different atoms, including carbon, oxygen, and
hydrogen. The radioactive isotope of carbon is
the familiar C-14 with ½ life 5730 yr. The
radioactive isotope of oxygen is O-15 with a ½
life of 122.2 s. The radioactive isotope of
hydrogen is called tritium and has a ½ life of
12.33 yr. The activity of each of these isotopes
is known at the time the bottle was sealed.
However, only one of the isotopes is useful for
determining the age of the wine. Which is it?
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31.8 Radioactive Decay Series
The sequential decay of one nucleus after another
is called a radioactive decay series.
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31.8 Radioactive Decay Series
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31.9 Radiation Detectors
A Geiger counter
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31.9 Radiation Detectors
A scintillation counter
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32.3 Nuclear Fission
A slowly moving neutron causes the uranium
nucleus to fission into barium, krypton, and
three neutrons.
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32.4 Nuclear Reactors
A nuclear reactor consists of fuel elements,
control rods, and a moderator.
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32.4 Nuclear Reactors
The moderator slows neutrons and the control rods
absorb neutrons.
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• The Standard Model
• The Building Blocks of Matter
• Quarks Make up Protons and Neutrons
• Leptons Most famous is the electron
• For every particle there is a corresponding
  antiparticle with an opposite charge
• Great Web Site http//particleadventure.org/parti
  cleadventure/index.html

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32.5 Nuclear Fusion
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32.6 Elementary Particles
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32.6 Elementary Particles
Pion production through p-p collision.
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32.6 Elementary Particles
Antiparticles, like positrons, can be used in
positron emission tomography, or PET scans.
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32.6 Elementary Particles
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32.6 Elementary Particles
Mesons consist of a quark-antiquark pair, while
baryons consist of three quarks.
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32.6 Elementary Particles
The current view of how matter is composed of
basic units.
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• The End
• Good Luck