Chapter 13: Turning Points Flashcards
What is an ether?
it was postulated as a fixed background
-all objects move with absolute motion relative to the ether
What was the name of the experiment that tested for the existence of the ether?
Michelson-Morley Experiment
What was the prediction of the Michelson-Morley experiment?
-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)
What was the aim of the Michelson-Morley experiment?
to find the difference between the speed of light ⊥ and ∥ light beams
-therefore find the absolute speed of Earth relative to the ether
What was the instrument which was used in the Michelson - Morley experiment?
-interferometer
What is the structure of the interferometer?
https://www.ecosia.org/images?q=interferometer%20diagram#id=42FB7FE4278D08A8C08F3F87B531CEA82F6A064A
also: to the right of the beam splitter, there is a plane glass sheet
What is the purpose of the beam splitter in the interferometer?
-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
What is the purpose of the plane glass sheet?
to allow for equal optical path length for the beams
What happens when the light beam leaves the source?
-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
What did Michelson & Morley do after the first set of results?
-they rotated the interferometer
- (swapping the ⊥ with the ∥ beam )
If an ether exists, what was the expected results of the interference pattern?
-expect the speeds to be different
-expect to see a small shift in the interference pattern
What were the actual results of the interference pattern?
no change in the interference pattern
proving that there was no ether
What is an inertial reference frame?
the frame of reference that is moving at constant or zero velocity- no acceleration
(follows Newton’s 1st law)
What are Einstein’s 2 postulates?
- the laws of physics are the same in all inertial frames of reference
- the speed of light in a vacuum is invariant
What is the thought experiment for special relativity? (light clock diagrams)
https://www.ecosia.org/images?q=special%20relativity%20light%20clock%20diagram#id=25615565D92C54E3C41B657EC425331C7640439A
What is proper length?
the length of an object measured by an observer at rest relative to the object
What effect does the muon decay experiment demonstrate?
time dilation
What was the expected result of the muon decay experiment?
expect most of the muons to decay before reaching sea-level
What was the actual result of the muon decay experiment?
most of the muons reached sea-level without decaying
What is the explanation for the results of the muon decay experiment?
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
What does this symbol represent and mean: m₀?
rest mass: mass of an object in its own inertial reference frame
What does this symbol represent and mean: m?
relativistic mass
As a particle approaches the speed of light, what happens to the mass?
the mass increases a lot
(amount of mass does not increase)
Why can no object reach the speed of light?
as an object approaches the speed of light, the mass increases so the force needed to accelerate the object gets larger
