Paper 3 - Option Module - Turning Points - 3.12.3 - Special Relativity

Question 1

3.12.3 - Special relativity

Question 2

3.12.3.1 - The Michelson-Morley experiment

Question 3

What permeated the whole universe?

Answer 3

The ether.

Question 4

What was the ether?

Answer 4

A substance that allowed the waves to travel, not getting in the way of rotating bodies.

Question 5

What were Michelson and Morley trying to test in their experiment?

Answer 5

How much the ether slowed the speed of light.

Question 6

What did Michelson and Morley use for their experiment?

Answer 6

An interferometer.

Question 7

What did the interferometer allow?

Answer 7

The interference of light rays

Question 8

Sketch a labelled diagram of the set-up of the interferometer.

Answer 8

In page 8.

Question 9

What was the compensator used for the in the set-up?

Answer 9

Ensure that both beams travel through the same thickness of glass to prevent waves overlapping.

Question 10

What was the equipment used for in the observation of the experiment?

Answer 10

• Interference pattern was viewed through telescope.
• Bright fringe = 2 beams arrive in phase (constructive interference).
• Dark fringe = 2 beams arrive in antiphase, phase difference of Pi radians or 180 degrees. (Destructive interference).

Question 11

What was the expected result of the experiment?

Answer 11

Rotating apparatus through 90 degrees would swap beam directions relative to Earth’s absolute motion = fringe shift.

Question 12

What was the actual result of the experiment?

Answer 12

Unable to detect fringe shift.

Question 13

What was the conclusion to the Michelson and Morley experiment?

Answer 13

Ether does not exist.

Speed of light is invariant in free space - independent of the motion of source or observer.

Question 14

What is a null result?

Answer 14

A result that does not support the hypothesis.

Question 15

What is absolute motion?

Answer 15

The translation of a body from absolute place to another, but this is not true.

Question 16

3.12.3.2 Einstein’s theory of special relativity

Question 17

What is a frame of reference?

Answer 17

A set of coordinates used to determine positions and velocities of objects in that frame or stage.

Question 18

What is an inertial frame of reference?

Answer 18

Those which move at constant velocity, not undergoing any acceleration or rotation, obeying Newton’s laws.

Question 19

What is meant by the term postulate?

Answer 19

Assumption.

Question 20

What are Einstein’s two postulates of special relativity?

Answer 20

1. Speed of light in free space = invariant.
2. Laws of physics have the same form in all inertial frames of reference.

Question 21

3.12.3.3 Time dilation

Question 22

What is proper time?

Answer 22

The amount of time that has passed, experienced by the stationary observer.

proper time = to.

Question 23

State the time dilation equation.

Answer 23

Found in equation data sheet.

to > t.

Question 24

Who measures the proper time, to, in the the time dilation equation?

Answer 24

Whoever is at both events (moving from A to B), is the person that measures proper time, to.

Question 25

Explain how muons are evidence for time dilation and special relativity.

Answer 25

We observe that a muon takes longer than 2.2 microseconds to decay, giving its time to reach Earth’s surface.

Question 26

3.12.3.4 Length Contraction

Question 27

Define proper length.

Answer 27

The proper length of an object is the length measured by the observer, who is at rest relative to the moving object.

Proper length = lo.

Question 28

State the equation for length contraction.

Answer 28

Found in the data sheet.

lo > l.

Question 29

What will remain constant in length contraction?

Answer 29

The width of the object, experiencing a change in length.

Question 30

3.12.3.5 Mass and Energy

Question 31

What is larger - the relativistic mass of a moving object, or its rest mass (mo)?

Answer 31

Relativistic mass.

Question 32

What is the equation that links the relativistic mass to the rest mass of an object?

Answer 32

In page 10 of notes.

Question 33

Sketch the graph of relativistic mass against speed.

Answer 33

In page 10 of notes.

Question 34

How do you calculate total energy?

Answer 34

Total energy = KE + rest energy.

Question 35

What is the equation that links total energy to proper/rest mass?

Answer 35

In page 11 of notes.

Question 36

What is the equation for KE, given the total energy and rest mass?

Answer 36

In page 11 of notes.

Question 37

Sketch a graph of KE against speed.

Answer 37

Page 20.

Question 38

What was Bertozzi’s experiment?

Answer 38

To measure the speed of electrons with different kinetic energies.

Question 39

How did Bertozzi measure the speed of electrons?

Answer 39

• electrons released in pulses.
• time taken to travel between detectors, calculated by distance between two peaks on oscilloscopes.
• Then get distance between detectors.
• Speed = distance/time.

Question 40

How did Bertozzi accelerate the electrons?

Answer 40

Particle accelerator was used to emit the electrons at different/various KE.

Question 41

How did Bertozzi calculate the KE of each electron?

Answer 41

KE of each electron = mc(delta theta) / n.

n = no. of electrons in pulse.
electrons collide with target, so KE is transferred to heat, and change in temp of target is measured using temperature sensor.

Question 42

What relationship did Bertozzi find between the KE and speed of the electrons?

Answer 42

Values were very close to those predicted by Einstein’s theory of special relativity.