Unit 3 HW 2 (Complete)
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Dec 6, 2023
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PHYS 1403
C. R. James
UNIT 3 HW #2
Description:
The figure below shows a train traveling toward the right and sounding
its horn. Three persons are shown at locations A, B, and C. Assume that all three
people can hear the train blowing its horn.
1.
Ranking Instructions:
Rank the pitch of the horn from highest pitch (or frequency)
to lowest pitch (or frequency) as heard by each person (A – C)
Ranking Order:
Highest
C
A
B
Lowest
Or, the pitch heard by each person would be the same.
(indicate with check
mark).
Carefully explain
your reasoning for ranking this way:
Looking at this chart, you can see the sound barriers represented by the dotted lines.
Person A would be the first to hear the sound. The next person to hear the sound be
Person C, due to the train moving towards Person C, the sound would carry over. Finally,
Person B would be the last to hear it.
2.
Ranking Instructions:
Rank the wavelength (from longest to shortest) of the sound of
the horn as heard by each person (A – C).
Ranking Order:
Longest
B
A
C
Shortest
Or, the wavelength heard is the same for each person.
(indicate with check mark).
Carefully explain
your reasoning for ranking this way:
I chose this ra
nking because the pitch would get higher due to the higher frequency
waves.
Description:
The figure below shows the motion of five distant stars (A - E) relative to
a stationary observer (telescope). The speed and direction of each star is indicated by
the length and direction of the arrows shown.
C
E
A
D
Observer
Distant Stars
Ranking Instructions:
Rank the Doppler shift of the light observed from each star (A –
E) from greatest “blueshift”, through no shift, to greatest “redshift”.
3. Ranking Order:
Greatest blueshift
E
,
D
,
B
C
A
Greatest
redshift
Or, the Doppler shift for each star is the same.
(indicate with check mark).
Carefully explain
your reasoning for ranking this way:
I chose this option because when a star moves to you, you can see the
wavelengths that it gives off. So when a star moves towards you, it’s a blueshift.
The only stars that is facing you (the observer) is Stars E and D. If it moves away,
it becomes a red shift, so Stars B, C, and A are more red.
B
4.
COMPLETE p 86, questions 4-5 of Lecture Tutorials (Doppler Shift exercise) and insert
answers/images below:
4.
a.
I think Star A would be a blueshift.
b.
Star B would be a redshift.
c.
Star C would not have a shift at all.
5. I agree with Student 2. The spectra of the stars will tell you if the star is moving away
or towards you.
5.
COMPLETE p 87, questions 6-7 of Lecture Tutorials (Doppler Shift exercise) and insert
answers/images below:
6. Spectra C is moving towards you. Despite Spectra A being similar, Spectra C is more
closer to the blue end of the spectrum compared to Spectra A.
7. Spectra B is moving away. I chose this because it’s spectra is in the red more than
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Spectra A and C.
6.
COMPLETE p 87 – 88, questions 8-9 of Lecture Tutorials (Doppler Shift exercise) and
insert answers/images below:
8. Assuming that F is the “Resting” position, I assume that Star G is the one that moved
the fastest. It’s coming towards us, since it’s mostly in the blue category (so its a
blueshift).
9. Star D would be the one that is moving the slowest. It’s moving away from us, so it’ll
be a redshift.
7.
COMPLETE p 88 – 89, question 10 (a-e) of Lecture Tutorials (Doppler Shift exercise)
and insert answers/images below:
10.
a.
Star L is blueshifted. (smallest number on the list.)
b.
Star I is redshifted. (Biggest number)
c.
Star L is near the Earth, while Star I is away.
d.
Stars H and L would appear blue. Stars I and K would be red.
e.
Star L is closet to Eath and Star I is farthest from Eath.
8.
How do astronomers determine the luminosity class of a star? What are the luminosity
classes? If a star is designated as a B3III star, what does this mean? (be as specific as
possible)
Astronomers determine the luminosity class by looking at the sharpness of the spectral
lines. This would mean that if the star is a B3III, it is a giant star.
9.
Star A has extremely strong, wide hydrogen lines. Star B has extremely strong, but
narrow hydrogen lines. Which star is hotter? Which star is larger? Which star is more
luminous? Explain your reasoning.
Star B would be the hotter of the two, but Star A would be the larger. Additionally, Star A
would be the luminous one because it is the bigger one of the two.
10.
In cluster HR diagrams (e.g. the Pleiades, 47 Tuc, etc…), what value is plotted on the y-
axis? Could you plot a useful HR diagram with random stars in the night sky using this
value? Why or why not?
The absolute magnitude of the stars is plotted on the y-axis. I think you would be fully
able to make a useful HR diagram with random stars. Assuming that you know the basic
idea of how luminosity with stars works, you can create a HR diagram.
11.
What is a visual binary? How do astronomers determine the orbital period of a visual
binary?
A visual binary is a binary star system that can be seen as two stars. Astronomers
determine the period of a visual binary by watching eclipsing and the measure time
between them.
12.
What is an eclipsing binary? How do astronomers determine the orbital period of an
eclipsing binary?
An eclipsing binary is when a star passes in front of and behind each other as seen from
Earth. Astronomers determine the orbital period of a eclipse binary by using the
combined brightness of the pair being reduced when one of the stars is hidden by the
other.
13.
If an O-type star is in a binary orbit with a similar-sized G-type star, where would the
LEAST light be detected from the system?
The least light would come from the G-type star when it passes in front of the O-star.
14.
What is a spectroscopic binary?
How do astronomers determine the orbital period for a
spectroscopic binary?
A spectroscopic binary is a binary system that appears as a star from Earth, but with
spectral lines that shows a doppler shift as star orbits. Astronomers determine the orbital
period of the binary by looking at the temperature.
15.
How do astronomers determine the masses of stars? Draw an HR diagram indicating
where main sequence LOW mass stars and HIGH mass stars are.
The masses of the stars are determined by the orbit of the binary stars.