Download Quantum Physics Cumulative Review

Quantum Physics Cumulative Review
AP Physics
Name:
Period:
Answer the following questions on your own sheet of paper.
Conceptual Review:
1. How was Einstein able to apply Planck’s idea that light waves had quantized energy to explain why
some wavelengths of light could knock electrons off a block of a particular metal and create a
photocurrent and others couldn’t?
2. How does the law of Conservation of Energy apply to a light beam hitting an electron on a metal and
knocking it off? Where is the energy before the light hits the metal and where is it afterward?
3. Helium-Neon [HeNe] lasers are very common lasers that emit 632.8 nm red light. How is it possible
for the neon atoms inside the laser (which are the ones that give off the light) to give off one particular
wavelength instead of a continuous spectrum with a range of frequencies.
4. a) Define fluorescence and phosphorescence.
b) Give an example of each phenomenon.
5. All lasers bear warnings to avoid shining them into anyone’s eyes. This is because the bright light
produced by a laser might cause damage to the back of someone’s eye. Why is a laser’s light bright
enough to be dangerous, even when they run at lower power than an incandescent bulb?
6. How can we understand Heisenberg’s statement that it is impossible to precisely know an object’s
position and momentum at the same time?
7. How would the periodic table change if electrons could have three different spins (-1/2,0,1/2) instead
of two?
Calculation Review:
1. Magnesium metal has a work function of 3.68 eV. You try shining different colors of light on a piece
of magnesium to get it to produce a photocurrent.
a) What wavelength should you measure as the cutoff wavelength for magnesium?
b) How much kinetic energy would an ejected photoelectron have if you shone 300 nm light on the
magnesium?
2. You try to get a photocurrent by shining 163 nm light on an unknown metal. When you do, you find
that you need to apply a voltage of 3.7 V to stop the ejected electrons. What is the work function of
the metal?
3. a) Find the wavelength of each photon after it scatters of a free electron:
i) A 0.052 nm photon scatters at a off an
ii) A 0.039 nm photon scatters at a off an
electron at a 60° angle
electron at a 150° angle
b) Which photon loses more energy when it hits the electron?
4. An electron orbits the nucleus in a Bohr hydrogen atom. Calculate radius, speed and energy for each
of the following orbits:
a) n = 4
b) n = 8
5. Based on your previous results, what wavelength photon is produced when the electron in a hydrogen
atom drops from the 8th energy level to the 4th energy level?
6. You take measurements of the spectrum of an atom whose ground state has the outermost electron in
an orbit with -5.25 eV of energy. You discover that the atom emits two visible lines in its spectrum
when the outermost electron is excited, with wavelengths of 420 nm and 690 nm respectively.
a) Draw an energy level diagram showing the different possible orbits for the electron that show up in
the data and label the energy of each orbit.
b) Are there any other wavelengths of light that the electron could emit? If so, what wavelengths?
7. Answer the following questions based on your previous results.
a) What is the DeBroglie wavelength for an electron orbiting in the 8th energy level of a Bohr
hydrogen atom?
b) How many DeBroglie wavelengths does it take to stretch all the way around the circulference of
the 8th energy level of a Bohr hydrogen atom?
8. A 10 g paper airplane is measured to fly at precisely 6 m/s.
a) What is the DeBroglie wavelength for the plane?
b) If we take the DeBroglie wavelength as our minimum uncertainty in the location of the plane, what
is the minimum uncertainty in the momentum of the plane? What is our uncertainty in the speed of the
plane?
9. An electron is excited to the (4,0,0) orbit in its atom.
a) How many different wavelengths of light could it produce when it dropped to a lower energy level
if it were the sole electron in a helium ion?
b) How many different wavelengths of light could it produce when it dropped to a lower energy level
if it were one of the electrons in a neutral helium atom?
c) How many different wavelength of light could it produce when it dropped to a lower energy level if
it were one of the electrons in a neutral helium atom in a strong magnetic field?