Download PRS Questions (queestions after Midterm 2)

PRS Questions
(queestions after Midterm 2)
PRS question: Thermal Radiation
The graph below shows the blackbody spectra of three different stars.
All three stars have the same size. Which of the stars is at the
highest temperature?
1.
1) Star A
2) Star B
3) Star C
Brightness
A
Hotter objects emit more total radiation per unit
surface area.
 Stephan-Boltzmann Law
4
 E = σT
B
C
Wavelength
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PRS question: Thermal Radiation
The graph below shows the blackbody spectra of three different stars.
All three stars have the same size. Which of the stars is at the
highest temperature?
•
1) Star A
2) Star B
3) Star C
Brightness
A
Hotter objects emit bluer photons (with a higher
average energy.)
 Wien Law
 λmax = 2.9 x 106 / T(K)
[λmax in nm]
B
T(K) = 2.9 x 106 / λmax [nm]
C
λmax
λmax
Wavelength
PRS: The Doppler Effect
Two identical stars are moving towards the Earth. Star A’s emission
lines (that are normally at visible wavelengths) are observed to be
at ultraviolet wavelengths. Star B’s emission lines are observed to
be at X-ray wavelengths. From these observations you conclude
that:
1) both stars are moving away from the Earth
2) Star A is moving towards the Earth faster than Star B
3) Star B is moving towards the Earth faster than Star A
4) Star B is actually moving away from the Earth
2
Uranus is almost 20 times farther from
the Sun than the Earth. Consider one of
the moons of Uranus that has no
atmosphere. How much colder is the
surface of that moon compared to the
surface of the Earth’s Moon?
1.
2.
3.
4.
5.
20 times colder
40 times colder
200 times colder
400 times colder
1000 times colder
I’d like to know
the answer to
this PRS Question
The sunlight that we
actually measure
• Flux = energy per area
per second
• Area of a sphere = 4πR2
• Flux = Luminosity
4πR2
If we somehow know the luminosity
and we measure the flux, we can solve
for the distance to the object!
3
Uranus is almost 20 times farther from
the Sun than the Earth. How much lower
is the flux of Sunlight at Uranus
compared to the flux at the Earth?
1.
2.
3.
4.
5.
20 times lower
40 times lower
200 times lower
400 times lower
1000 times lower
Flux = Luminosity
4π R2
The things that a telescope must do...
Our eyes work via the process of:
1) transmission
2) reflection
3) absorption
4) emission
5) none of the above
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Consider a gas cloud in space, such
as the one shown at right. Suppose
that it starts to collapse suddenly.
What will happen to the
temperature of the cloud as
PRS it collapses?
1. The cloud will cool down.
2. The cloud will warm up.
3. The cloud temperature will remain the
same.
4. This cannot be answered without
additional information.
PRS
PRS
PRS. Which of the following
principles of physics is NOT
important for understanding the
formation of the Solar System?
1.
2.
3.
4.
5.
Conservation of angular momentum
Conservation of linear momentum
Conservation of energy
Newton’s law of gravity
Actually, all of these laws of physics
are important factors
This is an extra-credit prs, as explained in lecture.
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PRS Question:
Look carefully at this
picture. What might you
conclude about the way
that Saturn formed?
1. Tidal forces due to encounters
between Saturn and comets/asteroids
are the main origin of the rings
2. Saturn is a “mini solar system”. The
physics that led to the formation of the
rings are the same as those that formed
the Sun and its planets, etc.
Note: we didn’t do the PRS question this semester, but it is a useful
question to think about:
PRS Question:
Why are Saturn’s rings
confined to a thin plane?
1. Tidal forces
2. Newton’s 1st law
3. Conservation of energy
4. Conservation of angular momentum
angular momentum = m x v x r
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What happens next?
• Kinetic energy = 1/2 mv2
PRS Question:
Consider a balloon full of air. Inside that
balloon, which of the following elements
will move the slowest?
1.
2.
3.
4.
Hydrogen (atomic weight = 1)
Helium (atomic weight = 4)
Nitrogen (atomic weight = 14)
Oxygen (atomic weight = 16)
14N
is a stable isotope with atomic
number = 7 and atomic mass = 14
What happens when carbon-14 radioactively decays
into nitrogen-14?
PRS question
1.
2.
3.
4.
The carbon becomes ionized
A proton turns into a neutron
A neutron turns into a proton
Neutrons and protons both change forms
“Parent” isotope
14C
radioactive
(6 protons, 8 neutrons)
decay
“Daughter” isotope
14N
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Radioactive Decay
• When a radioactive isotope suddenly
changes, the process is called radioactive
decay.
• Most common carbon isotope: carbon-12
(6 protons & 6 neutrons). Stable isotope.
• Radioactive carbon isotope: carbon-14
(6 protons & 8 neutrons)
“Parent” isotope
14C
radioactive
(6 protons, 8 neutrons)
decay
“Daughter” isotope
14N
(7 protons, 7 neutrons)
Radioactive decay half-life
• Half-life: the amount of time required for half
of the parent nuclei in a solid to decay
PRS QUESTION. Suppose that one year you put 10 kilograms of a
radioactive isotope in a cabinet in your laboratory. The stuff has a
half-life of 10 years. If 30 years later you stumble across that stuff,
you will find that you still have
1.
2.
3.
4.
5.
7.5 kilograms of the radioactive isotope
5.0 kilograms of the radioactive isotope
2.5 kilograms of the radioactive isotope
1.25 kilograms of the radioactive isotope
0.625 kilograms of the radioactive isotope
8
PRS Question:
The inside of the Earth is
1. Entirely molten rock, i.e., “magma”
2. Entirely solid rock
3. Mostly magma with a small amount of
solid rock
4. Mostly solid rock with a small amount of
molten rock
PRS Question: How were these maps of
the atmospheric ozone obtained?
Much of these data were collected by
“TOMS”, the “Total Ozone Mapping
Spectrometer”
1.
2.
3.
NASA has airplanes flying
around the atmosphere
measuring the amount of ozone
NASA has balloons floating in
the ozone layer collecting
samples
NASA observes the spectrum
of the atmosphere with a
telescope
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