Special Relativity Quiz

Einstein’s First Postulate states that:

• The laws of physics are the same in all inertial frames of reference.

• The laws of motion only apply when objects move slowly.

• Light behaves differently in different frames.

• Forces change depending on the observer’s speed.

Answer explanation

Einstein’s First Postulate asserts that the laws of physics are consistent across all inertial frames, meaning they do not change regardless of the observer's state of motion. This makes the first choice the correct answer.

Einstein’s Second Postulate states that the speed of light in a vacuum:

• Depends on how fast the source is moving.

• Depends on how fast the observer is moving.

• Is constant for all observers regardless of motion.

• Doubles if the source is moving towards you.

Answer explanation

Einstein’s Second Postulate asserts that the speed of light in a vacuum is constant for all observers, regardless of their motion. This means that light's speed does not change based on the movement of the source or observer.

Jimmy drives with his headlights on at 20 m/s. According to relativity, how fast does someone in the car measure the speed of light from the headlights?

• c – 20 m/s

• c

• c + 20 m/s

• 0.5c

Answer explanation

According to the theory of relativity, the speed of light is constant in all frames of reference. Therefore, someone in the car measures the speed of light from the headlights as c, not affected by the car's speed.

A stationary observer sees time appear to run slower on fast-moving objects.

• True

• False

Answer explanation

True. According to the theory of relativity, a stationary observer perceives time on fast-moving objects as running slower due to time dilation, which occurs at high velocities.

To a stationary observer, moving objects appear longer in the direction of motion.

• True

• False

Answer explanation

The statement is false. According to the theory of relativity, moving objects actually appear shorter in the direction of motion to a stationary observer, a phenomenon known as length contraction.

The “proper time” is:

• The time measured by the outside observer.

• The time measured in the moving object’s own frame (shortest time).

• The time measured only on Earth.

• The longest possible time between events.

Answer explanation

The "proper time" refers to the time measured in the moving object's own frame, which is the shortest time between events according to the theory of relativity. This makes it the correct choice.

The “dilated time” measured by a stationary observer is:

• Always shorter than the proper time.

• Always longer than the proper time.

• The same as the proper time.

• Only used for light.

Answer explanation

In relativity, proper time is the time measured by a clock moving with the observer. A stationary observer measures dilated time, which is always longer than the proper time due to time dilation effects.

A spacecraft travels at 0.70c. The pilot measures 5.0 hours for the journey. What type of time does the pilot measure?

• Dilated time

• Proper time

• Relative time

• Invariant time

Answer explanation

The pilot measures proper time, which is the time experienced by an observer in their own frame of reference. Since the pilot is on the spacecraft, the 5.0 hours is the proper time for the journey.

Atomic clocks flown on aircraft run slightly slower compared to clocks on Earth. This is:

• Evidence for time dilation.

• A measurement error.

• Due to faulty equipment.

• Because planes are in stronger gravity.

Answer explanation

The observation that atomic clocks on aircraft run slightly slower than those on Earth is consistent with the theory of relativity, which predicts time dilation due to relative motion and gravitational effects. Thus, it is evidence for time dilation.

Muons created in the atmosphere reaching Earth’s surface is real-world evidence that moving clocks run slower.

• True

• False

Answer explanation

True. Muons, which are unstable particles created by cosmic rays, travel at speeds close to light. Due to time dilation, they can reach the Earth's surface before decaying, demonstrating that moving clocks (muons) run slower compared to stationary ones.