Modern Physics Homework: Quantum Physics
Use the GUESS METHOD and turn in all calculations on a separate sheet of paper
Quantum Energy Practice Problems:
, where E is energy, h is Planck’s constant, and ƒ is frequency
Recall:

Useful conversions: 1 eV = 1.6x10-19 J

h = 6.63x10-34 J•s = 4.14x10-15 eV•s
1.
Assume that the pendulum of a grandfather clock acts as one of Planck’s resonators. If it carries away an
energy of 8.1x10-15 eV in a one quantum change, what is the frequency of the pendulum? (Note that an
energy this small would not be measureable. This is why we do not notice quantum effects in the largescale world).
2.
A vibrating mass-spring system has a frequency of 0.56 Hz. How much energy of this vibration is carried
away in a one-quantum change?
3.
A photon is a laboratory experiment has an energy of 5.0 eV. What is the frequency of this photon?
4.
Radiation emitted from human skin reaches its peak at λ = 940 µm.
a. What is the frequency of this radiation?
b. What type of electromagnetic waves are these? (Refer back to your electromagnetic spectrum
activities)
c. How much energy (in electron volts) is carried by one quantum of these electromagnetic waves?
The Photoelectric Effect Practice Problems:
, where KEmax is maximum kinetic energy, h is Planck’s constant, ƒ is
frequency, and is the work function
1.
In the photoelectric effect, it is found that incident photons with energy 5.00 eV will produce electrons with
a maximum kinetic energy 3.00 eV. What is the threshold frequency of this material?
2.
Light of wavelength 350 nm falls on a potassium surface, and the photoelectrons have a maximum kinetic
energy of 1.3 eV. What is the work function of potassium? What is the threshold frequency for potassium?
3.
Calculate the work function of sodium using the information given in the Pencast example for the
Photoelectric Effect.
4.
Which of the following metals will exhibit the photoelectric effect when light of 7.0x10 14 Hz frequency is
shined on it?
a.
b.
c.
Lithium, = 2.3 eV
Silver, = 4.7 eV
Cesium, = 2.14 eV