physics exam 3
according to the big bang theory, how did the universe begin?
rapid expansion of spacetime from a very dense initial state.
on what path does light travel in flat spacetime
straight line path
What predictions were made by the Big Bang hypothesis that were later confirmed by observation?
- Primordial abundance of helium - Cosmic microwave background
What problems with the Big Bang theory would be difficult to solve without cosmic inflation? Choose all that apply.
- Uniform temperature of the CMB - Flatness of the Universe - Foamlike structure of galaxy superclusters
Suppose car A & car B are both moving 60 mph northbound. what is Car B's velocity in Car's A reference frame?
0 mph
Suppose a person is walking down an escalator. The escalator is moving 2 mph upward with respect to the ground, and the person is walking 3 mph downward with respect to the escalator. What is the person's velocity with respect to the ground?
1 mph downward
suppose a person is walking down an upward-moving escalator. The escalator is moving 2 mph upward with respect to the ground, and the person is walking 3mph downward with respect to the escalator. What is the person's velocity with respect to the ground?
1 mph downward
Order each form of energy according to its abundance in the Universe, from most (1) to least (5)
1. dark energy 2. dark matter 3. hydrogen 4. helium 5. everything else
Suppose car A is moving 60 mph, and car B is moving 70 mph, both northbound, as measured from the ground. What is car B's velocity relative to Car A
10 mph northbound
Suppose car A is moving 60 mph, and car B is moving 70 mph, both northbound, as measured from the ground. What is car A's velocity relative to Car B
10mph southbound
suppose you are on a ground escalator that is moving left 2mph. you are walking right at 3 mph with respect to the escalator. what is your velocity in the ground's frame of reference?
1mph to the right
suppose you are on a ground escalator that is moving right at 2.6 mph. you are walking right at 1.2 mph with respect to the escalator. How fast are you walking relative to the ground?
3.8
How many dimensions are in spacetime?
4
suppose you are walking on a ground escalator that is moving left at 3mph. you are walking left at 1.6 mph relative to the escalator. how fast are you walking relative to the ground?
4.6 mph to the left
suppose a person is walking down an upward-moving escalator. The escalator is moving 2 mph downward with respect to the ground, and the person is walking 3mph downward with respect to the escalator. What is the person's velocity with respect to the ground?
5 mph downward
Which photon has more energy?
A photon with frequency 500 THz
Which electron has the shorter de Broglie wavelength?
An electron flying near lightspeed
According to the quantum model of the atom, which of the following best describes an electron in an atom?
An electron is a standing wave (cloud) surrounding the nucleus.
Which of the following best describes the nature of an electron? Assume time is linear.
An electron is both a particle and a wave.
What is dark matter?
An unseen source of gravity
According to experiment, which interpretation correctly describes the fundamental nature of reality?
Both interpretations are equally supported by experiment.
How do we know there is hydrogen in the Sun's atmosphere
By observing the Sun's spectral lines.
Why can an electron microscope see smaller objects than an optical microscope?
Electrons have smaller wavelength than visible light
According to observational evidence, how did the Universe begin?
From an explosion of spacetime and energy
Suppose an electron in an atom jumps from energy level 2 to energy level 4. Where does it get the energy needed to do this?
It absorbs a photon.
Suppose an electron in an atom drops from energy level 3 to energy level 1. What happens to the lost energy?
It is emitted as a photon.
Suppose I measure an electron's velocity with high precision. How precisely, then, do I know its position?
Only vaguely
According to the Copenhagen interpretation of quantum physics, how is quantum uncertainty explained?
Particles are physical waves disturbing the matter field
According to the Many Worlds interpretation of quantum physics, how is quantum uncertainty explained?
Particles behave randomly and probabilistically because linear time is an illusion.
Which of the following pieces of evidence in favor of the Big Bang Theory has NOT been observed?
Photographs of the Universe immediately after the Big Bang
What is the advantage of quantum computers over traditional computers?
Qubits instead of bits
In what sense is faster-than-light travel consistent with physics?
Spacetime itself can move faster than light.
How do we know there is hydrogen in the Sun's atmosphere?
The Sun's spectrum contains hydrogen spectral lines.
According to the Quantum Model of the atom, what is an electron?
Wave or cloud surrounding the nucleus
What is dark energy?
Whatever is causing the Universe's expansion to accelerate
What happens to an electron's wave packet when it's measured?
collapses
What do we all the faster-than-light expansion that occurred shortly after the Big Bang?
cosmic inflation
according to general relativity, what is gravity?
curvature of spacetime
On what path does light travel in a region of strong gravity?
curved
According to Einstein's theory of general relativity, what is gravity?
curved spacetime
What is causing the Universe's expansion to accelerate today?
dark energy
What is the most abundant form of energy in the Universe?
dark energy
dark matter or dark energy: Pushes galaxies apart
dark energy
dark matter or dark energy: The most abundant form of energy in the Universe
dark energy
Dark Matter or energy: Dominates on the scale of galaxies and galaxy clusters
dark matter
Dark Matter or energy: Invisible source of gravity
dark matter
What do we call the unseen source of gravity that surrounds galaxies?
dark matter
suppose you are on a spaceship traveling 0.9c. You shoot a laser beam at Earth. At what speed will the beam strike the Earth?
exactly c
Consider an electron moving freely in deep space. Before it's measured, what happens to its wave packet?
expands
true or false: Gravity has no effect on light.
false
Suppose you're on Earth, monitoring a space ship that's flying by at 0.5 c. In the pilot's reference frame, the ship is 100 meters long. How long is the ship in your reference frame?
less than
suppose you are on a spaceship flying toward Earth at one-quarter lightspeed (0.25c). In your frame of reference, your ship is 15m long. How long is your ship as seen from Earth's surface?
less than 15m
Suppose you're on a space ship traveling toward Earth at 0.5 c. You shoot a proton beam at Earth. The beam leaves your ship at 0.9 c. At what speed will the beam strike the Earth? Recall that protons have mass.
less than C
suppose you are on a spaceship traveling 0.9c. You shoot an electron beam at Earth. The beam leaves your ship at 0.5c. At what speed will the beam strike the Earth?
less than c
Which of the following best describes the nature of light?
light is a particle and a wave
what does the equation E=mc^2 mean?
mass is a type of energy that can be converted to other types of energy
If you drop a clock into a region of very strong gravity, how quickly will you see the clock tick?
more slowly than normal
Is it possible to know an electron's exact position (that is, with no uncertainty)?
never
Is it possible to know an electron's exact velocity?
never
Suppose I perform a double-slit experiment on a single electron. Is it possible to predict where the electron will land?
no
Suppose you perform a double slit experiment with light. Is it possible to predict correctly where an individual photon will land?
no
Suppose I measure an electron's position with extreme precision. How precisely, then, can I know its velocity?
only vaguely
Suppose I measure an electron's position with high precision. How precisely, then, do I know its velocity?
only vaguely
Suppose I measure an electron's velocity with high precision. How precisely, then, do I know its position?
only vaguely
How would an electron best be classified?
particle and wave
suppose you are on a spaceship flying toward Earth at half-light speed (0.5c). you are communicating with your friend on Earth by radio. What will you notice about your friend's rate of speech?
they will appear to be speaking more slowly than normal
True or false: Time flows more slowly in a region of strong gravity.
true
Suppose I perform a double-slit experiment on 1,000 electrons. Is it possible to predict the pattern they will make when they land?
yes
Suppose you perform a double slit experiment with light. Is it possible to correctly predict the interference pattern?
yes
suppose you are on a spaceship flying toward Earth at half-light speed (0.5c). you are communicating with your friend on Earth by radio. What will your friend notice about your rate of speech?
you will appear to be speaking more slowly than normal
Suppose I am in an inertial reference frame. What is my velocity, as measured from my own frame?
zero
