Almost all detection of visible light is by the

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Almost all detection of visible light is by the
photoelectric effect (broadly defined.) There
is always a threshold photon energy for
detection, even in film.
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Blackbody radiation
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A
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A particle in a box of width 2L has the
wavefunction shown. By what factor is the
particle more likely to be in the right side of
the box, compared with the left side?
A equally likely B twice as likely C four
times as likely D eight times as likely
C
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A particle in a box of width 2L has the
wavefunction shown. What is the probability of
the particle being found in the right side of the
box?
A 50 B 66.6 C 75 D 80
D
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A particle in a box of width 2L has the
wavefunction shown. What is the constant
a?(Use pencil paper.)
A 1 B C D
D
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Note Measuring the particles position may (in
fact does) change the wavefunction. More on this
later
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For a free particle with wave functionWhat is
the direction of wave motion?A -xB xC
no direction- its a stationary state
A
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For a free particle with wave functionWhat is
the sign of the momentum? A -B C the
momentum is zero
A
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For a free particle with wave functionWhere
is the particle?A at the origin (x0)B not
necessarily at, but near the originC
somewhere, but we dont know exactly whereD
everywhere at once
D (not C!)
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For a free particle with wave functionIs this
a stationary state?A yesB noC cant
tell
A
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Wave packets
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Wave packets
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Wave packets
B
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Summary (so far)

• What is complicated about quantum mechanics
• Particles must have (or be) waves. Equations that
  describe waves are more mathematically
  complicated than Fma. But how waves behave is
  classical. If you can understand waves in water
  or sound, you can understand QM waves. (For
  example, classical waves are quantized like
  waves on a violin string.)
• What is simple and beautiful in QM
• Matter and light have the same description, a
  hybrid of wave and particle.
• What is unfathomable in QM
• How do we know when to switch between a
  particle description and a wave description? This
  switch seems to occur when we measure the
  position of a photon or electron then, it acts
  like a particle, and the wave associated with it
  collapses to its measured location.

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• What is n for the state shown?
• A 1
• B 2
• C 4
• D 8
• E 0

C
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• If a measurement of the particles position is
  made, what are the relative probabilities that it
  will be found in regions A, B, and C?
• Note the wavefunction is drawn offset from zero.
  We often draw the zero of the wavefunction at the
  energy of the state.
• A all regions are
• equally probable
• B region A is most
• probable, then B, then C
• C region B is most
• probable, then A C tie
• D region B is least
• probable, AC tie

D
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• At a later time, the probability of finding the
  particle at B will be larger than finding it at A
  or C.
• A true
• B false

False.
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• After measuring the position of the particle, it
  will still be in this wavefunction or state.
• A true
• B false

False.
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• After measuring the energy of the particle, it
  will still be in this wavefunction or state.
• A true
• B false

True.
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• A measurement is made of the momentum of the
  particle.
• What are the results?
• A 0
• B with equal
• probability

B
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• Correspondence principle How could this EVER
  LOOK LIKE a classical particle, bouncing around
  inside a box?
• Answer(s)
• We need to consider a wavepacket,
• And
• Macroscopic systems are never in pure energy
  states.
• (Pure states are called eigenstates)

http//groups.physics.umn.edu/demo/applets/qm1d/in
dex.html
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All things are waves, obeying wave
equations. Measurement (which is NOT precisely
defined in QM!) changes the wave. It collapses
it to a wave appropriate to the measured value.
The best possible measurement of energy puts a
system in an energy eigenstate, which we
also call a stationary state When in a
stationary state, the probability density is
stationary. Absorption and Emission of light by
atoms is (apparently) such an energy
measurement. Some folks think measurement
means a conscious observer observes, but QM is
NOT precise about what a measurement is. If
measurement requires a conscious observer, you
get odd things, like Schroedingers Cat. There
are almost no restrictions on what an arbitrary
wavefunction looks like. (Must be finite,
continuous, and have a continuous derivative if
Ultinfinity.) In general, wavefunctions are not
stationary states (or any special state, like a
state of precise p.)
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Suppose we have a superposition
wavefunction The probability of measuring an
eigenvalue is proportional to the Magnitude
squared of the coefficient of that eigenfunction.
Correspondence principle The behavior of
wave packets with high quantum numbers looks
classical.
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Harmonic potential. (A spring.) The effect of
the widening of the potential at higher energies
is to make the energy eigenstates equally spaced.
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Energy eigenstates of the harmonic potential.
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Which is the n3 energy eigenstate?
B
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A particle is in a bound energy eigenstate in a
finite square well. A measurement of the
particle position finds it in the classically
forbidden region.In this region, the potential
energy is higher than the particles (original)
total energy.Explanation??
A energy (and momentum) are not precisely
conserved in QM B the particle was in a
classically allowed spot, but the
measurement perturbed it C the particle is
still in the same energy state, so energy is
conserved D the measurement adds energy to the
particle in an unspecified way
D
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A particle is in a bound energy eigenstate in a
finite square well. A measurement of the
particle position finds it in the classically
forbidden region.After the measurement
A the particle will be in the same bound energy
eigenstate B the particle will be in a different
bound energy eigenstate C the particle will be
in superposition of bound states D the particle
will be unbound
C or D
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A particle is in a bound energy eigenstate in a
finite square well. A measurement of the
particle position finds it in the classically
allowed region.After the measurement
A the particle will be in the same bound energy
eigenstate B the particle might still be
bound C the particle must be unbound
B
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Tunneling In the barrier, the wavefunction
decays exponentially. How should I draw the
wave on the other side of the barrier?
A There is no wave on the other side B The
wave on the other side should have the same
wavelength, but a smaller amplitude C The wave
on the other side should have the same amplitude,
but a smaller wavelength D The wave on the
other side should have a smaller amplitude and a
larger wavelength E None of these is correct
B
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In this simulation, Why is the energy of the
wavepacket shown as a green schmear?
A The exact kinetic energy of the wavepacket is
unknown. B In order for tunneling to occur, the
wavepacket must have some energies (or energy
components) higher than the barrier C
Wavepackets intrinsically contain a spread of
energies.
C
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In this simulation, If I make the wavepacket
bigger, what do you think will happen to the
energy schmear?
A It will get narrower B It will stay the
same C It will get broader
A
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In this simulation, What will happen to the
wavelength on the right if I lower the potential
energy there?
A It will be shorter than the wavelength on the
left B it will remain equal to the wavelength
on the left C it will become longer than the
wavelength on the left
A.
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Radioactive decay is tunneling
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