Unit 3 HW 2(1) (2) (5)
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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 1
A
2
C
3
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:
A would receive the highest pitch since he would hear the horn's "best" pitch. Shorter wavelengths
correspond to higher pitches, hence C's in front so he may hear the waves continuing from the train after B
heard them.
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 1
B
2
A
3
C
Shortest
Or, the wavelength heard is the same for each person.
(indicate with check mark).
Carefully explain
your reasoning for ranking this way:
The wavelengths lengthen as B follows the train as it travels away from him.
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
1
A
, 2
B
, 3
D
,
4
C
,
5
E
Greatest redshift
Or, the Doppler shift for each star is the same.
(indicate with check mark).
Carefully explain
your reasoning for ranking this way:
A appears to being moving towards the direction of red
B
4.
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)
a.
I = Super Giants, II = Bright Giants, III = Giants, IV = Subgiants, V = Main
Sequence, B3II is a hot giant star.
5.
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.
a.
A is more luminous because it is bigger than B and almost as hot, while B is
hotter because A is larger.
6.
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?
a.
No, in terms of luminosity, they aren't just randomly placed stars in the sky since
then the data wouldn't be very consistent and you'd have stars that may deviate in
both ways from the norm.
7.
What is a visual binary? How do astronomers determine the orbital period of a visual
binary?
a.
Two stars of varying brightness, while watching the stars' true orbits
8.
What is an eclipsing binary? How do astronomers determine the orbital period of an
eclipsing binary?
a.
Rare binary-star system in which one star is frequently seen passing in front of
the other, eclipsing the other star, and allowing for the study of its light curve
from Earth
9.
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?
a.
when an O type star is in front of a G star.
10.
What is a spectroscopic binary?
How do astronomers determine the orbital period for a
spectroscopic binary?
a.
The temperature of a binary system that from Earth seems to be a single star but
whose spectral lines exhibit back and forth Doppler changes as two stars circle.
11.
How do astronomers determine the masses of stars? Draw an HR diagram indicating
where main sequence LOW mass stars and HIGH mass stars are.
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