Chapter 13: Turning Points

Question 1

What is an ether?

Answer 1

it was postulated as a fixed background
-all objects move with absolute motion relative to the ether

Question 2

What was the name of the experiment that tested for the existence of the ether?

Answer 2

Michelson-Morley Experiment

Question 3

What was the prediction of the Michelson-Morley experiment?

Answer 3

-motion of the Earth through the ether would affect the speed of light
(depending on whether the light travelled ⊥ or ∥ to the Earth’s motion)

Question 4

What was the aim of the Michelson-Morley experiment?

Answer 4

to find the difference between the speed of light ⊥ and ∥ light beams
-therefore find the absolute speed of Earth relative to the ether

Question 5

What was the instrument which was used in the Michelson - Morley experiment?

Answer 5

-interferometer

Question 6

What is the structure of the interferometer?

Answer 6

https://www.ecosia.org/images?q=interferometer%20diagram#id=42FB7FE4278D08A8C08F3F87B531CEA82F6A064A
also: to the right of the beam splitter, there is a plane glass sheet

Question 7

What is the purpose of the beam splitter in the interferometer?

Answer 7

-to allow 1/2 the light to be transmitted
-1/2 of the light gets reflected
this creates 2 identical beams of light travelling ⊥ to each other

Question 8

What is the purpose of the plane glass sheet?

Answer 8

to allow for equal optical path length for the beams

Question 9

What happens when the light beam leaves the source?

Answer 9

-passes through the beam splitter
-2 ⊥ beams
-beams get reflected at the plane mirrors
-beams return to the beam splitter
-they undergo superposition
-create an interference pattern

Question 10

What did Michelson & Morley do after the first set of results?

Answer 10

-they rotated the interferometer
- (swapping the ⊥ with the ∥ beam )

Question 11

If an ether exists, what was the expected results of the interference pattern?

Answer 11

-expect the speeds to be different
-expect to see a small shift in the interference pattern

Question 12

What were the actual results of the interference pattern?

Answer 12

no change in the interference pattern
proving that there was no ether

Question 13

What is an inertial reference frame?

Answer 13

the frame of reference that is moving at constant or zero velocity- no acceleration
(follows Newton’s 1st law)

Question 14

What are Einstein’s 2 postulates?

Answer 14

1. the laws of physics are the same in all inertial frames of reference
2. the speed of light in a vacuum is invariant

Question 15

What is the thought experiment for special relativity? (light clock diagrams)

Answer 15

https://www.ecosia.org/images?q=special%20relativity%20light%20clock%20diagram#id=25615565D92C54E3C41B657EC425331C7640439A

Question 16

What is proper length?

Answer 16

the length of an object measured by an observer at rest relative to the object

Question 17

What effect does the muon decay experiment demonstrate?

Answer 17

time dilation

Question 18

What was the expected result of the muon decay experiment?

Answer 18

expect most of the muons to decay before reaching sea-level

Question 19

What was the actual result of the muon decay experiment?

Answer 19

most of the muons reached sea-level without decaying

Question 20

What is the explanation for the results of the muon decay experiment?

Answer 20

to the Earth based observer:
-time passes slower for the muons because of their relativistic speeds
-so the muons have a longer relativistic half-life
-so more muons reach sea-level without decaying

Question 21

What does this symbol represent and mean: m₀?

Answer 21

rest mass: mass of an object in its own inertial reference frame

Question 22

What does this symbol represent and mean: m?

Answer 22

relativistic mass

Question 23

As a particle approaches the speed of light, what happens to the mass?

Answer 23

the mass increases a lot
(amount of mass does not increase)

Question 24

Why can no object reach the speed of light?

Answer 24

as an object approaches the speed of light, the mass increases so the force needed to accelerate the object gets larger

Question 25

What is the experiment to prove that no object can reach the speed of light?

Answer 25

accelerating electrons to very high speeds and measuring their specific charge

Question 26

How does the mass of an object increase?

Answer 26

by transferring energy to it
E=mc²

Question 27

What does E₀ mean?

Answer 27

the rest energy

Question 28

What components is the total energy made up of?

Answer 28

-rest energy
-kinetic energy

Question 29

What is the formula for the kinetic energy in terms of relativistic mechanics?

Answer 29

KE= mc² - m₀c²
-mc²: total energy
-m₀c²: rest energy

Question 30

What is the relationship between relativistic mass and proper mass?

Answer 30

m=ɣm₀
-the smallest mass is proper mass

Question 31

What is the relationship between relativistic length and proper length?

Answer 31

L=L₀ / ɣ
-the longest length is the proper length

Question 32

What is the relationship between relativistic time and proper time?

Answer 32

-t=ɣt₀
-the shortest time is the proper time

Question 33

Describe Bertozzi’s experiment?

Answer 33

1. Pulses of electrons are produced
2. Electron beams are detected between a known distance
3. T.O.F measured with an oscilloscope
4. Each pulse raises the temperature of the Al
5. The temp. rise can be measured by a thermocouple
6. E=mcΔΘ/ n
   where n is the number of electrons

Question 33

Describe Bertozzi’s experiment?

Answer 33

1. Pulses of electrons are produced
2. Electron beams are detected between a known distance
3. T.O.F measured with an oscilloscope
4. Each pulse raises the temperature of the Al
5. The temp. rise can be measured by a thermocouple
6. E=mcΔΘ/ n
   where n is the number of electrons

Question 34

What is the set-up for Bertozzi’s experiment?

Answer 34

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