PHYS 187 Final Exam questions with
correct answers
A star's luminosity is the
surface temperature of the star
lifetime of the star
total amount of light that the star radiates each second
total amount of light that the star will radiate over its entire lifetime apparent brightness of the
star in our sky - correct answer ✔✔total amount of light that the star radiates each second
What is the approximate composition of the Sun?
50 percent hydrogen, 25 percent helium, 25 percent other elements
100 percent hydrogen and helium
70 percent hydrogen, 28 percent helium, 2 percent other elements
70 percent helium, 28 percent hydrogen, 2 percent other elements
98 percent hydrogen, 2 percent helium and other elements - correct answer ✔✔70 percent
hydrogen, 28 percent helium, 2 percent other elements
Suppose you put two protons near each other. Because of the electromagnetic force, the two
protons will
remain stationary.
repel each other.
collide.
,join together to form a nucleus.
attract each other. - correct answer ✔✔repel each other
The spectral sequence in order of decreasing temperature is
BAGFKMO.
OBAGFKM.
ABFGKMO.
OFBAGKM.
OBAFGKM. - correct answer ✔✔OBAFGKM
Why do astronomers often measure the visible-light apparent brightness instead of the total
apparent brightness of a star?
In order to measure the total apparent brightness of a star, you must measure its brightness in
all wavelengths, and this is difficult to do. The only wavelengths you can measure from the
surface of Earth are visible and radio wavelengths.
Most stars do not put out light in other ranges of the spectrum.
Astronomers are lazy.
they are identical for most stars.
All stars put out most of their light in the visible range of the spectrum. - correct answer ✔✔In
order to measure the total apparent brightness of a star, you must measure its brightness in all
wavelengths, and this is difficult to do. The only wavelengths you can measure from the surface
of Earth are visible and radio wavelengths.
Thermal radiation is defined as ________.
,radiation with a spectrum whose shape depends only on the temperature of the emitting
object.
radiation produced by an extremely hot object.
radiation that is felt as heat.
radiation in the form of emission lines from an object. - correct answer ✔✔radiation with a
spectrum whose shape depends only on the temperature of the emitting object.
How does the explosion of a nuclear bomb provide evidence of the theory of relativity?
The bomb causes things in its vicinity to move at very high speeds, allowing scientists to
measure effects of time dilation.
The mass of the bomb when it explodes is much greater than its normal mass.
The bomb shortens the lifetimes of all people who happen to be near it when it detonates.
The bomb produces energy in accord with E = mc2, which is part of the theory of relativity. -
correct answer ✔✔The bomb produces energy in accord with E = mc2, which is part of the
theory of relativity.
On a Hertzsprung-Russell diagram, where would we find red giant stars?
lower right
upper left
upper right
lower left - correct answer ✔✔upper right
Why do the predicted consequences of the special theory of relativity seem so strange to most
of us?
because they are self-contradictory, making it impossible to make any sense of them
, because they are obvious only at speeds that we never experience in our daily lives
because they contradict the well-tested ideas of Newton's laws of motion
because they affect only subatomic particles and not big things like people - correct answer
✔✔because they are obvious only at speeds that we never experience in our daily lives
In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot thanks to
gravitational contraction. What was the major drawback of this idea?
It is physically impossible to generate heat simply by making a star shrink in size.
It predicted that the Sun would shrink noticeably as we watched it, and the Sun appearss to be
stable in size.
It predicted that the Sun could last only about 25 million years, which is far less than the age of
Earth.
It predicted that Earth would also shrink, which would make it impossible to have stable geology
on our planet. - correct answer ✔✔It predicted that the Sun could last only about 25 million
years, which is far less than the age of Earth.
Which of the following statements about thermal radiation is always true?
A hot object emits photons with a longer wavelength than a cool object.
A hot object emits photons with a higher average energy than a cool object.
A hot object emits more radio waves than a cool object.
A hot object emits more X rays than a cool object. - correct answer ✔✔A hot object emits
photons with a higher average energy than a cool object.
If you see Jackie going to your left at exactly 0.99c and Bob going to your right at exactly 0.99c,
Jackie will say that Bob is
going away from her at 1.98c.
correct answers
A star's luminosity is the
surface temperature of the star
lifetime of the star
total amount of light that the star radiates each second
total amount of light that the star will radiate over its entire lifetime apparent brightness of the
star in our sky - correct answer ✔✔total amount of light that the star radiates each second
What is the approximate composition of the Sun?
50 percent hydrogen, 25 percent helium, 25 percent other elements
100 percent hydrogen and helium
70 percent hydrogen, 28 percent helium, 2 percent other elements
70 percent helium, 28 percent hydrogen, 2 percent other elements
98 percent hydrogen, 2 percent helium and other elements - correct answer ✔✔70 percent
hydrogen, 28 percent helium, 2 percent other elements
Suppose you put two protons near each other. Because of the electromagnetic force, the two
protons will
remain stationary.
repel each other.
collide.
,join together to form a nucleus.
attract each other. - correct answer ✔✔repel each other
The spectral sequence in order of decreasing temperature is
BAGFKMO.
OBAGFKM.
ABFGKMO.
OFBAGKM.
OBAFGKM. - correct answer ✔✔OBAFGKM
Why do astronomers often measure the visible-light apparent brightness instead of the total
apparent brightness of a star?
In order to measure the total apparent brightness of a star, you must measure its brightness in
all wavelengths, and this is difficult to do. The only wavelengths you can measure from the
surface of Earth are visible and radio wavelengths.
Most stars do not put out light in other ranges of the spectrum.
Astronomers are lazy.
they are identical for most stars.
All stars put out most of their light in the visible range of the spectrum. - correct answer ✔✔In
order to measure the total apparent brightness of a star, you must measure its brightness in all
wavelengths, and this is difficult to do. The only wavelengths you can measure from the surface
of Earth are visible and radio wavelengths.
Thermal radiation is defined as ________.
,radiation with a spectrum whose shape depends only on the temperature of the emitting
object.
radiation produced by an extremely hot object.
radiation that is felt as heat.
radiation in the form of emission lines from an object. - correct answer ✔✔radiation with a
spectrum whose shape depends only on the temperature of the emitting object.
How does the explosion of a nuclear bomb provide evidence of the theory of relativity?
The bomb causes things in its vicinity to move at very high speeds, allowing scientists to
measure effects of time dilation.
The mass of the bomb when it explodes is much greater than its normal mass.
The bomb shortens the lifetimes of all people who happen to be near it when it detonates.
The bomb produces energy in accord with E = mc2, which is part of the theory of relativity. -
correct answer ✔✔The bomb produces energy in accord with E = mc2, which is part of the
theory of relativity.
On a Hertzsprung-Russell diagram, where would we find red giant stars?
lower right
upper left
upper right
lower left - correct answer ✔✔upper right
Why do the predicted consequences of the special theory of relativity seem so strange to most
of us?
because they are self-contradictory, making it impossible to make any sense of them
, because they are obvious only at speeds that we never experience in our daily lives
because they contradict the well-tested ideas of Newton's laws of motion
because they affect only subatomic particles and not big things like people - correct answer
✔✔because they are obvious only at speeds that we never experience in our daily lives
In the late 1800s, Kelvin and Helmholtz suggested that the Sun stayed hot thanks to
gravitational contraction. What was the major drawback of this idea?
It is physically impossible to generate heat simply by making a star shrink in size.
It predicted that the Sun would shrink noticeably as we watched it, and the Sun appearss to be
stable in size.
It predicted that the Sun could last only about 25 million years, which is far less than the age of
Earth.
It predicted that Earth would also shrink, which would make it impossible to have stable geology
on our planet. - correct answer ✔✔It predicted that the Sun could last only about 25 million
years, which is far less than the age of Earth.
Which of the following statements about thermal radiation is always true?
A hot object emits photons with a longer wavelength than a cool object.
A hot object emits photons with a higher average energy than a cool object.
A hot object emits more radio waves than a cool object.
A hot object emits more X rays than a cool object. - correct answer ✔✔A hot object emits
photons with a higher average energy than a cool object.
If you see Jackie going to your left at exactly 0.99c and Bob going to your right at exactly 0.99c,
Jackie will say that Bob is
going away from her at 1.98c.
