Intro Modern Cosmos RQ 2
If the frequency of a certain wave is 10 hertz, its period is
0.1 seconds
A spaceship passes by the earth with Boot factor 10. Proper length of the space is 5 meters. What is the length of the space ship as measured by an observer on the Earth?
0.5meters
A spaceship passes by the earth with Boot factor 4. What will be the velocity of the spaceship relative to the earth.
0.97 c
Comparing diameters, the Sun is about ______ times larger than the Earth.
100
The temperature at the Sun's core is about _____.
15,000,000 K
a rocket passes by earth at a speed of 0.8c and the length of the rocket as measured by an observer on earth is 100m
167m
An object that completes 20 vibrations in 10 seconds has a frequency of
2 hertz.
Calculate the Schwarzschild radius for the Sun. Here's what to do: 1. Use M = 1 solar mass = ______ kg, use the number you looked up in the previous problem. 2. To get an answer in meters, use G = 6.67 x 10-11 and c = 300,000,000 . 3. Plug the numbers into the formula RS = 2 G M / c2 .
2,964 m
Calculate the escape velocity from a neutron star. Here's what to do: 1. Look up the mass of the Sun in kilograms (one 'solar mass'). 2. Assume the mass of the neutron star is two solar masses, M = 2 x (answer from 1). 3. Assume the radius of the Neutron Star is 10,000 meters (= R). 4. With these units, use G = 6.67 x 10-11 . 5. Calculate the escape velocity in m/s by plugging the above numbers into the formula vesc =
231,000,000 m/s
A wave travels an average distance of 6 meters in two seconds. What is the wave's velocity?
3 m/s
A space ship passes by with Boost factor = 4, and you see the ship has length L = 80 meters. What is the proper length as see by an observer in the spaceship?
320 meters
The Sun will leave the main sequence in about ______ years from now.
5 billion
Which of the following is the only possible value of the Boost factor ?
6/4
If a blue star emits light with a peak wavelength of 400 nm, what is its surface temperature in kelvin? Hint: Use Wien's law, T = (2.9 x 106 K nm) / (lmax) where l is the Greek letter lambda representing wavelength.
7250 K
The Sun is a distance of 150 million kilometers from Earth, calculate how long light takes to travel from the Sun to Earth. Hints: Look up the speed of light in units of km/s. Calculate the time in seconds using T = D/V. Convert that time to minutes.
8.3 min
Your body temperature is about 300K, at what wavelength do you radiate most strongly? Hint: Same formula as last time, T = (2.9 x 106 K nm) / (lmax) but now you are given T and solving for lmax. Aside: This radiation is in the infrared part of the electromagnetic spectrum and explains why you glow when seen by infrared cameras or infrared-seeing animals like rattlesnakes.
9670 nm
Which of these is NOT homogeneous?
A page from a book.
The star Aldebaran is a red giant and is much more luminous than the Sun. What conclusions can be drawn from this fact?
Aldebaran is cooler than the Sun, but has larger diameter than the Sun
Which of the following statements about planetary nebulas is correct?
All of the above: They are shells of glowing gas and dust ejected by dying Sun-like stars. They contain flakes of carbon and silicon material. Their shape can be very irregular.
Gravitational waves
Are traveling distortions of space and time
Which of the following stars has the hottest stellar surface temperature?
B2
Which of the following is closest in size (diameter ) to a neutron star?
Bakersfield (city)
The Sun's atmosphere consists of the _____ and the _____.
Chromosphere; corona
A train is traveling along a straight, horizontal track at a constant speed that is only very slightly less than that of light. A warning light on the ground flashes once each second. An observer in the train measures the time between flashes to be
Greater than one second.
Why do white dwarfs have high temperatures?
Heat left over from their formation.
The Sun is mostly made of this element.
Hydrogen
What is the difference between emission and absorption in terms of what happens to an electron in an atom?
In emission, the electron falls into a lower orbit, closer to the nucleus; in absorption the electron is boosted to a further-out orbit.
How can a space traveller make a trip of 4 light-years to Alpha Centauri in less than 4 years without exceeding the speed of light?
In her frame, the distance is contracted to less than 4 light years.
A protostar is not _____.
In hydrostatic equilibrium
Where do most of the elements heavier than iron form?
In supernova explosions.
If it were possible to move a star closer to the Earth then its apparent brightness would ______ while its absolute magnitude number would _______.
Increase; stay the same
Which of the following is not true of the Space-time interval ?
It can only apply to simultaneous events
If a star is in hydrostatic equilibrium
Its radiation pressure outwards and gravitational forces inwards are in balance.
What stars live the longest?
K and M
A man watches a football game from the window of a fast-moving train with constant velocity parallel to the football field. Using Galilean relativity, the man would measure the field at the usual 100 yards and the duration of the period - after adjusting for the travel time of light - to be the usual 15 minutes. Using special relativity, what length would he measure for the field?
Less than 100 yards.
Protostars turn into
Main-Sequence Stars.
Which of the following statements is wrong?
Mass and energy are equivalent in Newtonian view
A man watches a football game from the window of a fast-moving train with constant velocity parallel to the football field. Using Galilean relativity, the man would measure the field at the usual 100 yards and the duration of the period - after adjusting for the travel time of light - to be the usual 15 minutes. Using special relativity and again correcting for the travel time of light, what duration of time would he measure for the period?
More than 15 minutes.
A neutron star is made of neutrons, where do these neutrons come from?
Mostly from the merging of protons and electrons during core collapse.
Is the cosmological principle consistent with the existence of a center or an edge to the universe?
No, the distance of a location from center or edge would make locations fundamentally unequal.
In the Sun, nuclear fusion occurs
Only in the core.
The sunlight we receive on the Earth originates from the Sun's
Photosphere.
Lorentz transformation reduces to Galilean transformation in the limit of
Relative velocities of two inertial frames are small compared to the speed of light
The difference between time according to a clock on the Earth and a clock on a spaceship moving at nearly the speed of light relative to the Earth is best explained by
Special Relativity
The difference in how far a Muon (short-lived particle) travels in a particle accelerator before decaying is best explained by
Special Relativity
The principle of reciprocity relates the views of two observers in different frames according to?
Special Relativity
What are the axes of an H-R diagram
Surface temperature and luminosity.
According to cosmological principle :
The universe is homogeneous and isotropic.
How is the composition of the Sun today different than when it formed 4.6 billion years ago?
There is now more helium and less hydrogen.
Stars on the main sequence have different luminosities because
They have different masses
Without any air resistance, a feather and hammer dropped side-by-side, what should happen?
They will fall equally fast.
In discussing special relativity, we consider a phenomenon from the viewpoint of
Two inertial systems
When do we say that a star is born?
When fusion of hydrogen atoms into helium atoms start.
What is left when a planetary nebula dissipates?
White Dwarf
When the outer envelope of a red giant is ejected, the remaining exposed core of a low mass star is called a
White dwarf.
The "ultimate question of existence" is not just "why do things exist?", it is
Why does a universe of space and time exist?
The surface temperature of the Sun can be measured using ____
Wien's law
Einstein suggested that the regular change (advance) in the perihelion of the planet Mercury could be explained by:
a distortion in spacetime caused by the gravity of the sun
according to the general theory of relativity, light and other radiation coming from a white dwarf or a neutron star should (and experiments shows that it does) exhibit
a gravitational redshift
According to the formula E=mc^2
a little bit of mass can be converted into a substantial amount of energy
A "photon" is
a particle of light.
From which of the following will a wave of light show the greatest gravitational redshift:
a white dwarf
from which of the following will a wave of light show the greatest gravitational redshift
a white dwarf
When a light wave leaves a region of strong gravity, compared to the same wave leaving a spaceship in empty space, the wave in strong gravity will have
all of above: a loner wavelength, a lower frequency, less energy, and a gravitational redshift
Which of the following is a remnant of a dying star?
all of above: white dwarfs, neutron star, and black hole
Doppler effect occurs when a source moves
all of the above: towards you, away from you, and either towards you or away from you
The colors of the visible spectrum can be measured in units of
all of the above: wavelength, frequency, and energy
We explain light today
as having both wave and particle behavior.
When Einstein proposed his General Theory of Relativity, he suggested some pretty strange ideas about space, time, and gravity. How did scientists in 1919 show that Einstein's theory described the behavior of the real world and wasn't just a crazy hypothesis?
by observing starlight coming close to the sun during an eclipse
When astronauts aboard the International Space Station (ISS) in space let go of an orange, it just floats there. Why is that?
by the ISS if falling around the earth, and in free fall, things feel no weight
according to the general theory of relativity, the presence of mass
causes a curvature (or warping) of spacetime
If left in isolation a white dwarf will eventually
cools off an become a black dwarf.
The hot gas gave off an ______ spectrum and from the emitted colors of light the astronomer could determine the _______ of the gas.
emission; composition
When an electric stove element is hot enough, it gives off a dull red glow. When it cools to the point that it no longer glows, it will
emit longer wavelength radiation.
If you are in a freely falling elevator near the top of a tall building, as the elevator falls, your weight would be:
equal to zero- you would be weightless
cosmological red shift is expected due to
expansion of the universe
The Sun produces its energy from
fusion of hydrogen into helium.
The X-ray part of the spectrum is directly in-between
gamma ray and ultraviolet.
what is a key reason that gravitational waves are so much harder to detect than electro-magnetic (e-m) waves
gravitational waves are much weaker than e-m waves, and therefore require very, very precise equipment to detect
The "hydrostatic equilibrium" of the Sun is the balance between ______ trying to shrink it and ______ trying to expand it.
gravity; gas pressure
The second-most common element in the Sun is
helium
A star's ______ is the most critical factor determining what happens in every phase of a star's life.
mass
Compared to radio waves, gamma rays have
more energy.
If an object's spectral lines are shifted to longer wavelengths, the object is
moving away from us.
What is in the nucleus of atoms?
neutrons and protons
The time that is required for a vibrating object to complete one full cycle is called
period
Because observers measure different values for the time of the same event, time is a
relative quantity
Because observers measure different values for the speed of the same object, speed is a(n)
relative quantity.
Our Milky Way Galaxy is what type of galaxy?
spiral
in 1959, pound and rebka did an experiment to test the prediction of einstein's theory of general relativity about the relationship between the pace of time and the strength of gravity. When two identical atomic clocks, one on the ground floor and one on the top floor, were compared
the clock on the ground floor ran a tiny bit slower
the equivalence principle (principle of equivalence) says that
the effects of gravity are equivalent to the effects of acceleration
in the first direct detection of gravitational waves by LIGO in 2015, the wave came from
the merge of two black holes
which of the following statements about the mass of a neutron star affects spacetime is correct
the neutron star mass will curve spacetime, light has to follow that curvature
according to einstein's general theory of relativity, the stronger a star's gravity
the slower times runs near it
in the formula E=mc^2, the letter c stands for
the speed of light
Edwin Hubble developed a classification scheme for galaxies. By what characteristic did he classify galaxies?
their shape
in discussing special relativity, we consider a phenomenon from the viewpoint of
two inertial systems
you are in a fast moving spaceship moving towards east and I am in another similar spaceship moving towards west. when we pass each other we do precise measurements to determine the lengths of our own and each other's spaceships. What do we determine?
we each find that our own spaceships are their normal lengths while the other's spaceship is contracted
your friend claims that, theoretically, special relativity allows you to make a journey of a million light-years in less than one year of your time. Is that correct?
yes, at near the speed of light, the million light-year distance can be contracted to less than one light-year in your frame
