Question 1

What is the meaning of the Schwarzschild radius around a black hole?

Accepted Answer

A)  It is the radius at which an orbiting object would show a precession. 
B)  It is the radius at which gravitational redshift can be detected. 
C)  It is the radius at which the black hole's spin equals the speed of light. 
D)  It is the radius at which the escape velocity equals the speed of light. 
E)  It is the radius at which a body falling onto the black hole would move at half the speed of light.

Question 2

Gamma-ray bursts are probably associated with extremely energetic supernova explosions.

Accepted Answer

A) True 
 B)False

Question 3

__________ is the result of mass distorting the fabric of spacetime.

Accepted Answer

A)  Energy 
B)  Radiation 
C)  Fusion 
D)  Gravity 
E)  Electric charge

Question 4

Special relativity says that all observers moving at constant speed will measure the same value of the speed of light.

Accepted Answer

A) True 
 B)False

Question 5

What will observers in different inertial frames of reference always agree on?

Accepted Answer

A)  how the speed of light varies with the motion of an observer 
B)  the length of the meter, but not the duration of the second 
C)  the rate each frame is accelerating 
D)  the results of physics experiments performed in each frame 
E)  whether events are simultaneous or not

Question 6

While traveling the galaxy in a spacecraft, you and a colleague set out to investigate a 10M _$\odot$ black hole. Your colleague hops aboard an escape pod and drops into a circular orbit around the black hole maintaining a distance of 50 km from it, while you remain much farther away inside the spacecraft. After doing some experiments to measure the strength of gravity, your colleague signals the results back to you using a green laser. What would you see, and why?

Accepted Answer

The answer of While traveling the galaxy in a spacecraft,...

Question 7

You repeatedly measure the radial velocity of what seems to be a single main-sequence star like the Sun, but find that it is in fact orbiting in a tight orbit around another object that remains unseen. From measurement of the velocity and orbital period, you calculate that the unseen object has a mass 20 times that of the Sun-like star. Why might this object be a black hole?

Accepted Answer

The answer of You repeatedly measure the radial velocity of...

Question 8

We can't detect the gravitational redshift coming from the Sun because the Sun has a very small amount of gravity.

Accepted Answer

A) True 
 B)False

Question 9

The aberration of starlight is:

Accepted Answer

A)  a change in the wavelength of light caused by the motion of the light source 
B)  poor focusing of starlight caused by imperfections in the optics of a telescope 
C)  a change in the direction of starlight caused by its passage through the earth's atmosphere 
D)  an increase in the wavelength of light as it leaves the surface of a gravitating body 
E)  a change in the direction of starlight caused by the orbital motion of the Earth

Question 10

Most black holes are found:

Accepted Answer

A)  by the watching the orbits of nearby stars 
B)  from the bending of the light from background stars 
C)  by finding objects that emit no light 
D)  by the X-rays produced by a surrounding accretion disk 
E)  by the detection of Hawking radiation

Question 11

What is true about muons?

Accepted Answer

A)  They are always moving at high speed, so they test relativity. 
B)  Relativity explains why we can see short-lived muons that are produced high in the atmosphere from cosmic rays. 
C)  We can see them being deflected from straight lines by the gravity of black holes. 
D)  They have a mass that does not increase if they are moving fast. 
E)  They are examples of Hawking radiation from black holes.

Question 12

One consequence of Einstein's ideas about the speed of light is that:

Accepted Answer

A)  if two events take place at the same time, all observers will see that event simultaneously 
B)  whether events are seen as simultaneous or not depends on the motion of an observer 
C)  observers will always disagree on when an event took place 
D)  it is not possible to know when an event happened 
E)  moving observers can always know whether they are in motion

Question 13

What is the central idea in relativity concerning the speed of light? Describe at least two unusual consequences of this idea.

Accepted Answer

The answer of What is the central idea in relativity...

Question 14

Two observers are on different floors of a building, as shown in the figure below. The observer on the bottom floor shines a light upward, which is reflected from a mirror in an upper floor and sent back downward. Consider the gravitational redshift of the light due to the Earth. If the light has a wavelength of exactly 600 nm when emitted, the observer on the upper floor will measure a wavelength of __________ while the observer on the lower floor will see the light returning with a wavelength of __________.

Accepted Answer

A)  "600 nm, 600 nm" 
B)  "$\gt$ 600 nm, 600 nm" 
C)  "$\lt$ 600 nm,$\lt$ 600 nm" 
D)  "600 nm, $\gt$ 600 nm" 
E)  "$\gt$ 600 nm, $\gt$ 600 nm"

Question 15

Hawking radiation from black holes refers to:

Accepted Answer

A)  light emitted from matter falling onto a black hole 
B)  the gravitational redshift of light emitted near the event horizon 
C)  the radiation of particles created near the event horizon 
D)  high-energy X-rays and gamma rays from the formation of a black hole 
E)  the optical and infrared light from an energetic supernova explosion

Question 16

Which of the following is a consequence of Einstein's special theory of relativity?

Accepted Answer

A)  Moving clocks run quicker. 
B)  The velocity of light depends on the speed of the observer. 
C)  Distances are shorter for objects traveling close to the speed of light. 
D)  Gravity arises because mass distorts spacetime. 
E)  Faster moving objects require less force to accelerate them.

Question 17

Explain one way we can detect black holes.

Accepted Answer

The answer of Explain one way we can detect black...

Question 18

Einstein's special theory of relativity implies that if a person standing at the front of a train traveling at 0.1 km/s shines a flashlight out in front of the train, the emitted photons will travel at a speed of 300,000.1 km/s.

Accepted Answer

A) True 
 B)False

Question 19

Why do astronauts in space feel no gravity?

Accepted Answer

A)  There is no gravity out in space. 
B)  Gravity only happens when objects are accelerating. 
C)  In space, the gravity from the Moon and the Sun cancels out the Earth's gravity. 
D)  They and their spaceship are both freely falling at the same rate in the gravitational field. 
E)  The astronauts do not have any mass when they are out in space.

Question 20

When do the predictions of special relativity match those of Newtonian physics?

Accepted Answer

A)  in terrestrial laboratories 
B)  inside our Solar System 
C)  when different observers are at rest with one another 
D)  when objects have a low mass 
E)  when objects are moving slowly

Exam 18: Relativity and Black Holes

What is the meaning of the Schwarzschild radius around a black hole?

Gamma-ray bursts are probably associated with extremely energetic supernova explosions.

__________ is the result of mass distorting the fabric of spacetime.

Special relativity says that all observers moving at constant speed will measure the same value of the speed of light.

What will observers in different inertial frames of reference always agree on?

We can't detect the gravitational redshift coming from the Sun because the Sun has a very small amount of gravity.

The aberration of starlight is:

Most black holes are found:

What is true about muons?

One consequence of Einstein's ideas about the speed of light is that:

What is the central idea in relativity concerning the speed of light? Describe at least two unusual consequences of this idea.

Hawking radiation from black holes refers to:

Which of the following is a consequence of Einstein's special theory of relativity?

Explain one way we can detect black holes.

Einstein's special theory of relativity implies that if a person standing at the front of a train traveling at 0.1 km/s shines a flashlight out in front of the train, the emitted photons will travel at a speed of 300,000.1 km/s.

Why do astronauts in space feel no gravity?

When do the predictions of special relativity match those of Newtonian physics?