Sample Exam questions:
Please note. Everything that we talked about in class is testable. This should not be considered an allinclusive list of topic to know but rather is to give you a feel for how I write test question. Just because a
topic isn’t included here, doesn’t mean I can’t test on it, it simply means I didn’t write an example
question on it.
Once again, this is NOT an all inclusive list. Please study your homework, the slides, videos, worksheets
and discussion worksheets.
When a metal was exposed to light at a frequency of 4.12x1015 Hz, electrons were emitted with a kinetic
energy of 5.50x10-19J. What is the work function of the metal? What is the maximum number of
electrons that could be ejected from this metal by a burst of light (at some other frequency) with a total
energy of 7.85x10-7J
2.18x10-18, 3.60x1011 electrons
Violet laser light occurs at a wavelength of 0.350 micrometers. A violet laser produces a pulse with an
energy of 0.250 J. What is the energy of the photons? How many photons are present in each pulse? If
the pulse takes 0.500 seconds, how many photons per second are released?
5.68x10-19 J
4.40x1017
8.81x1017
The work function for calcium is 7.53x10-19 J. What is the minimum frequency of light for the
photoelectric effect for calcium. Then calculate the kinetic energy of the ejected electron if the light of
frequency 1.60x1015 s-1 is used for irradiating the metal.
1.14x1015Hz
3.07x10-19 J
While repeating a photoelectric effect experiment you find the threshold frequency and then proceed to
increase the frequency of the incident radiation. What effect does this have on the number, energy and
speed of the ejected electrons? If you found the threshold frequency to be 7.74x1014Hz, what was the
value of the work function?
No effect on number of electrons, increased energy and increased speed
5.13x10-19J
Use the charts below to answer the following questions
a) Incandescent light bulbs (aka, the “old energy inefficient” lightbulbs), operate at a temperature of
between 2700 and 3300 K. Which would you expect to look “whiter” to the human eye the bulb
operating at 2700 or at 3300? 3300K
b) Why are incandescent bulbs inefficient light sources? Most of the energy emitted is in the IR region,
meaning that it is lost as heat rather than visible light.
c) Given that the sun approximates a black body radiator and is 5,900K, what color would you expect the
sun to be to the human eye? Does this agree with our everyday experience? Explain why if it does not.
White, disagree, higher energy light is scattered into the atmosphere by particulates, leaving the lower
energy reds, oranges and yellows to be seen directly from the sun.
Describe how scientists can use light from other stars to determine their temperatures.
Using Weins law the lambda max can be used to find the temperature (make sure you said something
about lambda MAX, or wavelength of maximum intensity, or some other way implied that there is more
than one wavelength coming off)
Explain the difference between destructive and constructive interference. How does this relate to the
young’s double slit experiment? (Adapted from slides, and previous exams)
Destructive= cancelling out/subtracting/lowering Constructive= increasing/adding
Gives interference patterns: bright=constructive dim=destructive
Who has the shorter wavelength when running at the same speed. A person weighing 130 pounds, or a
person weighing 100 pounds? Explain your logic. Why can’t we see the wavelength of macroscopic
objects. (adapted from bookwork and slides)
130: m is inversely propotional to mass; the wavelength is too small in comparison to the object
Using the following graph from class, explain why the grass is green. What would happen if you grew
plants under green light? Why? (Violet=400 nm, Indigo=445 nm, Blue= 475 nm, Green= 510 nm,
Yellow=570 nm, Orange=590nm, Red= 650 nm)
Most colors absorb; green is reflected (note: it is reflected
NOT emitted)
They’d die
Since they don’t absorb the light it cannot be used for
further reactions, i.e. no photosynthesis ect……
General Electromagnetic Spectrum
True or False: Visible light, which is of higher energy than IR radiation, also travels faster.
false
IR radiation has a lower energy than UV light, which has the longer wavelength?
IR
What is the wavelength of a microwave transmitting at 305 MHz?
0.983m
What is the wavelength of a radio station transmitting at 99.1 MHz?
3.03 m
In 1.0 s, a 30 W bulb emits 7.0 J of energy in the form of infrared radiation (heat) of wavelength 2120
nm. How many photons of infrared radiation does the lamp generate in 1.0 s?
7.5x1019
In 1.0 s, a 60 W bulb emits 11 J of energy in the form of infrared radiation (heat) of wavelength 1850 nm.
How many photons of infrared radiation does the lamp generate in 1.0 s?
1x1020
A team of scientists recently developed a series of nanowires that can act as miniature lasers. One
nanowire was found to emit light of frequency 8.73x1014Hz. What was the wavelength of the light?
3.43x10-7m
For the nanowire in the previous problem, what is the energy of the emitted radiation?
5.78x10-19J
Particle in a box.
Use the picture below of a particle in a box model to answer the following questions.
A)
B)
The graph labelled B represents: Probability density
The graph labeled A represents: Wavefunction
The energy level represented is: 3
The number of nodes equals: 2
Uncertainty Principle
Calculate the minimum uncertainty in position of a carbon atom moving 1.5*103 m/s that has
uncertainty of 10% of that value.
1.8x10-11m
If you decreased the uncertainty in the velocity, what happens to the uncertainty in the position?
Increases
What is the uncertainty in the position of an electron moving at 4.00x106 m/s with an uncertainty in
velocity of 1.00x104. (sapling)
5.79x10-9
If you decreased the uncertainty in the velocity, what would happen to the uncertainty in the position?
(adapted from slides)
increased
Wave or particle
Multiple choice: Young’s original double split experiment shows that light has _______ like nature
because:
A) Wave, because there are interference patterns
B) Wave, because there are two bright spots where the light goes through the slits
C) Particle, because there are interference patterns
D) Particle, because there are two bright spots where the light goes through the slits
E) Both, because there are interference patterns
F) Both, because there are two bright spots where the light goes through the slits
G) The wave or particle like nature of light cannot be determined
A
The original Young’s double split experiment supports which nature of light, wave or particle?
wave
If the frequency of light in a photoelectric effect is higher than the threshold frequency and it is
increased. What change, if any, will occur in the electrons?
Faster/more kinetic energy/higher velocity ect….
In Young’s double slit experiment the bright areas of light are due to. (two words)
constructive interference
DeBroglie Wavelength
Calculate the wavelength of a motorcycle of mass 275 kg traveling at a speed of 125 kmhr1
6.94x10-38m
Calculate the wavelength of a motorcycle of mass 452 kg traveling at a speed of 125 kmhr1
4.22x10-38m
Briefly (In no more than 6 words), explain why the wavelength of a chair or other macroscopic object
does not impact our interactions with the object.
Too small
True or false: Macroscopic items have a wavelength that is similar to the size of the object.
False
Mulder weighs 180 pounds, Scully weighs 140, both are running at the same speed. Who has the longer
wavelength? (adapted from slides)
scully
Wein’s Law
The planet Mercury has a maximum intensity of solar radiation of 3700 nm on the sunlit side. What is
the temperature of the surface of Mercury on the sunlit side?
784K
The temperature of a particular white dwarf star is 14300 K. What is the wavelength of maximum
intensity that the astronomer sees?
2.02x10-7m