1. Scientific Notation
Choose One • 5 points
Because quantum mechanics is physics that describes the interactions of very small
objects (i.e. molecules, atoms, and electrons), this week you will need to know how to
multiply very small numbers. Remember that scientific notation writes very small or
large number in terms of powers of 10. For example, .0008 can be written in scientific
notation as 8 x 10-4 or as 8E-4. The power of 10 (-4 in this case) tells you to take the
number 8.0 and move the decimal 4 places to the left giving us .0008.
Which is a correct representation of .000025 in scientific notation?
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2.5E-4
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2.5E-5
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2.5E-6
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25E-5
2. Scientific Notation
Choose One • 5 points
Let’s now multiply two numbers in scientific notation using Google.
Enter .0008 into Google exactly as it was written above as:
We could now multiply it by .000056 by typing:
Note that we have separated our two numbers by putting them inside parentheses, and
the * symbol (SHIFT+8) is used as the multiplication sign. We could have done a
division instead of multiplying by separating the two numbers by a forward slash
Multiply the number 4.48E-8 by 5.2E-4 using Google. What is the correct answer in
scientific notation?
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6.78E-11
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3.33E-12
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2.40E-12
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2.33E-11
3. Electron Transitions
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As mentioned in this week’s notes on page 4, the electrons of an atom can occupy
different energy shells within the atom (similar to how the planets all occupy different
orbits around the Sun). Electrons prefer to be in the lowest energy shell possible (the
ground state); however, they can gain energy and jump to a higher shell by absorbing
light or being excited by an electric current. In accordance with the conservation of
energy, if an electron drops from a higher energy level to a lower one, this must emit a
photon (particle of light) with energy equal to the energy difference of the shells.
A Balmer series transition is any transition of an electron from some higher energy shell
down to the second lowest energy shell (n=2) in hydrogen.
Looking at image (b) above, what is the wavelength of a photon emitted during the
Balmer transition from the n=3 shell in hydrogen? (remember nm is short for a
nanometer, for example 656 nm = 656 x 10-9 meters)
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656E-9 meters
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486E-9 meters
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434E-9 meters
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410E-9 meters
4. Momentum
Choose One • 5 points
Use the momentum equation for photons found in this week's notes, the wavelength you
found in #3, and Plank’s constant (6.63E-34) to calculate the momentum of this photon:
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1.0E-27 kgm/s
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1.8E-27 kgm/s
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2.0E-27 kgm/s
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3.0E-27 kgm/s
5. Frequency
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Use the equation from week 3:
frequency=wavespeedwavelength
and the wavelength you found in #3 to calculate the frequency of this photon (remember
the speed of light is 3E8 m/s):
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7.6E14 Hz
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6.0E14 Hz
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4.6E14 Hz
6. Energy
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Use the energy equation from this week’s notes, your answer from #5, and Plank’s
constant(6.63E-34) to find the approximate energy of this photon:
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4.8E-19 Joules
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3.0E-19 Joules
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3.0E-17 Joules
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1.21 Gigawatts
7. Atomic Spectra
Choose One • 5 points
A glass tube is filled with hydrogen gas. An electric current is passed through the tube, and
the tube begins to glow a pinkish/purple color (this is how fluorescent bulbs and neon
signs produce light). If you were to pass this pink light through a prism to separate the
individual light frequencies, you would see that this pink light is composed of four distinct
colors: violet, green, blue, and red. Notice the similarity between image (b) above and
image (b) from question #3.
Which is the best description of why this occurs?
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The electrons within the hydrogen atoms gain energy from the current
causing them to jump to higher energy orbitals. When they fall back to a lower
energy orbital they release a single proton. These protons have discrete energies
equal to the difference in energy of the two orbitals.
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Atoms contain continuous energy orbitals, meaning that the light the
hydrogen atoms produce can be of any energy. Depending on the type of prism
used, when the light reaches it, the prism will only allow specific light energies
(frequencies) to pass through.
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The light spectrum from any source contains all colors (frequencies) because
the Planck, constant, h, is so small.
8. Momentum and Energy
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The lights used by Mark Watley (played by Matt Damon) during the film The
Martian seem to be Metal Halide lamps. Metal Halide lamps are filled with vaporized
mercury and metal-halogen compounds. When an electric current is passed through
the lamp, the tube begins to glow a bright white/blue color. If you were to pass this light
through a prism to separate the individual light frequencies, you would see a rainbow
just as you would if using natural sunlight because of the complexity of the metal halide
gas and the vast amount of possible electron transitions.
(The study of light in this way is known as spectroscopy and allows astronomers to
know exactly what atoms compose distant stars, simply by looking at the light they
emit. The spectral lines an atom produces uniquely identifies that atom just like a
fingerprint uniquely identifies a person.
The momentum equation and energy equation that we have used above can be
combined to give the following equation:
c=Ep
where again p is the phonon momentum, E is the photon energy and c is the speed of
light. When you divide the photon energy found in #6 by the photon momentum found
in #4, do you get the speed of light?
(If not, check your work for questions #4 through #6).
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Yes
•
No
9. Light
Choose One • 5 points
All visible light (light that our eyes can detect) has wavelength between 400-700
nanometers. Wavelengths just smaller than 400 nm are Ultraviolet light. Wavelengths just
larger than 700 nanometers are infrared light. What type of light is the Balmer series light
that we have consider so far?
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Visible
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Ultraviolet
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Infrared
10. Light
Choose One • 5 points
The solar panels used by Mark function because of the photoelectric effect. Light shines on
the cells causing electrons to be ejected from the metal, which produces an electric
current. At night on Mars, no light will fall on the solar cells and no electric current will be
generated. According to your notes, what type of light is typically needed to cause the
photoelectric effect?
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Visible
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Ultraviolet
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Infrared
11. Balmer Series
Choose One • 5 points
If we were to illuminate them only with light from the Balmer transition considered above,
would the solar panels produce a current?
•
Yes
•
No
12. Balmer Series
Choose One • 5 points
Starting with only the Balmer series light (visible light), how could we ensure that the solar
panels generate a current that Mark can use for his power station? (It may help to look at
the electromagnetic spectrum from week 3):
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By gradually increasing the brightness (amount) of light that we shine on it.
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By gradually increasing the frequency of the light we shine on it.
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By gradually increasing the wavelength of the light that we shine on it.
13. Special Relativity
Choose One • 5 points
Imagine you are riding on a yacht in the ocean and traveling at 20 mph. You then hit a golf
ball at 100 mph from the deck of the yacht. You see the ball move away from you at
100mph, while a person standing on a near by beach would observe your golf ball traveling
at 120 mph (20 mph + 100 mph).
Now imagine you are aboard the Hermes spacecraft traveling at 0.1c (1/10 the speed of
light) past Mars and shine a laser from the front of the ship. You would see the light
traveling at c (the speed of light) away from your ship. According to Einstein’s special
relativity, how fast will a person on Mars observe the light to be traveling?
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0.1c (1/10 the speed of light)
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c (the speed of light)
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1.1c (c+0.1c)
14. Stellar Evolution
Choose One • 5 points
Note: The following questions are unrelated to the Balmer series or The
Martian. Please refer to your course notes.
A Sun-sized star will spend most of its lifetime as a:
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White Dwarf
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Red Giant
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Protostar
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Main-Sequence Star
15. Stellar Evolution
Choose One • 5 points
Our Sun will eventually:
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explode in a supernova.
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become a white dwarf star.
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become a black hole.
16. Stellar Evolution
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A main sequence star does not expand or contract due to the balance between the
internal heat pushing outward and the weight of the material pressing inward due to
gravity. This state of maintaining a constant size is known as:
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hydrostatic equilibrium
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thermal equilibrium
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dynamic equilibrium
17. Stellar Remnants
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Neutron stars are:
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Low density star remnants with many neutrons, which mass is less than the
mass of the Sun.
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Incredibly small remnants of super massive stars where the gravitational collapse
is stop by neutron degeneracy.
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Incredibly big and massive star remnants which expelled all its neutrons in a
supernova explosion.
18. Stellar Remnants
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Black holes are:
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Star remnants from super massive stars which gravitational collapse can not be
halt by electron or neutron degeneracy and gravity is so strong in their vicinity
that not even light can escape.
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Regions of the universe with space empty of matter or radiation that becomes so
dark that forbids us from investigating it.
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Regions of space where matters is not sufficiently hot to radiate in the visible
spectrum.
19. Newton vs. Einstein
Choose One • 5 points
Which of the following states that all matter tends to "warp" space in its vicinity and that
objects react to this warping by changing their paths?
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Newton's Universal Law of Gravitation
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Einstein's General Relativity
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Einstein's Special Relativity
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Newton's First Law of Motion
20. Quantum Mechanics
Choose One • 5 points
Wave-particle duality tells us that wave and particle models apply to all objects
whatever the size, so why don't we observe wave properties in macroscopic objects?
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Because their particle properties forbid us from observing their wave properties.
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Because their wavelength is extremely long (undetectable).
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Because their wavelength is extremely short (undetectable).