M7 Topic 4 Special relativity Flashcards Preview

Physics Year 12 > M7 Topic 4 Special relativity > Flashcards

Flashcards in M7 Topic 4 Special relativity Deck (22)
Loading flashcards...
1
Q

what is the classical physics understanding of light (3)

A
  • waves require a medium (aether)
  • light where considered as continuous waves due to their wave behavior (such as reflection refraction, diffraction and interference)
  • Maxwell predicted the speed of light 3x10⁸ms⁻¹
2
Q

What are the assumptions in Galilean Relativity (based on newtonian assuptions) (2)

A
  • The laws of motion are the same in all inertial frames of reference ( cannot do any experiment to determine if you are moving)
  • Relative velocity is calculated by adding vectors
3
Q

What were the issues with Galilean Relativity (2)

A
  • Implied that the speed of light was not constant and could be increased
  • Light was recorded to be constantly 3x10⁸ by Hertz
4
Q

What is the aether (2)

A
  • The medium of propagation for light, based of the wave model of light
  • Seen as the absolute frame of reference
5
Q

what was the justification for the aether model

A

Classical Physics, used the wave model of light due to light’s wave nature/behaviour (diffraction, refraction, reflection, interference)

6
Q

what are the features of the aether and their justifications

A
  1. Feature: Filled the universe
    Explanation: light was everywhere
    • Feature: Solid
    • Explanation: Propagate through solid due to light’s high speed)
    • Feature: Transparent
    • Explanation: Light energy was not diminished as it
      passed through the aether
    • Feature: Thin (very low density) and high elasticity
    • Explanation: Allow’s planets to move through it
      unimpeded(no friction)
7
Q

What is the significance of the aether (2)

A
  • The Earth would experience an aether wind as it moves at 30kms⁻¹ through space
  • Motion experiments on Earth would be relative to the aether( so it must be taken into account)
8
Q

What was the aim of the Michelson Morley experiment

A

Prove the existence of the aether, by identifying changes in the velocity of light , depending on its relative movement through space.

9
Q

how did the Michelson Morley experiment work (2)

A
  • A laser was shot at a half transparent mirror where two light beams will form
  • An interferometer was used to detect the difference in phases (interference pattern) between the two light beams that would have resulted in different travel times by rotating the apparatus.
10
Q

What were the results of Michelson Morley experiment

A

Michelson and Morley found NO change in the interference pattern at the interferometer as the apparatus was rotated through 90°

11
Q

What did the results in the Michelson Morley experiment mean (3)

A
  • The light beams arrived at the same time irrespective of their motion relative to the aether
  • results opposed the aether model of light transmission
  • provided evidence for Einstein’s theory of special relativity, and its theory of light transmission
12
Q

what is a frame of reference

A
  • The point of view or a perspective from where an observation can be made.
13
Q

What are inertial frames of reference

A

when the observer is not accelerating

14
Q

What are Einstein’s postulates of special relativity (2)

A
  1. All inertial frames of reference are equivalent (The laws of physics are the same in all inertial frames of reference).
  2. The speed of light (in a vacuum) is an absolute constant for all observers in an inertial frame of reference.
15
Q

What was Einstein’s thought experiment to explain special relativity

A
  • He questioned, if you were in a train that moved at the speed of light, would you be able to see your reflection in a mirror
16
Q

what was the answer to Einstein’s thought experiment to explain special relativity (2)

A

Yes you can see your reflection as:

  • Galilean relativity states that in a inertial frame of reference you cannot do an experiment, that can determine if you are moving or not.
  • Light is moving at constant, therefore observers outside of the frame of reference would see the train contract (length contraction) and time move slower in the train( time dilation)
17
Q

What was Einstein’s explanation of Simultaneity within special relativity

A
  • Simultaneity was relative, therefore no reference frame is correct (each perspective will see something different)
18
Q

What was Einstein’s example thought experiment of relativity

A

A train is moving close to the speed of light and there are two observers one outside the train and on inside the train, lightning strikes on both the front and the back of the train, what does each observer see?

19
Q

what was the result to Einstein’s thought experiment to explain relative simultaneity (2)

A
  • The observer outside the train sees the lightning strike both the front and the back simultaneously, as the lightning is in the same frame of reference
  • The observer inside the train sees the lightning at the front strike first and the back second as the train is moving towards light emitted from the front and moving away from the lighting at the back
20
Q

What was Einstein’s example thought experiment of time dilation

A

The light clock: a train moves close to the speed of light, a light source shines a light which is reflected off a mirror which reflects onto another mirror directly below it, and there are two observers one in the train and one outside, what does each observer see

21
Q

What was the result to einstein’s thought experiment of time dilation (2)

A
  • Observer in the train is in the same frame of reference as the light clock , and sees the proper time ( the shortest possible amount of time t₀)
  • Observer outside the train sees the clock ticking more slowly than the other observer as the approaching mirror is moving away from where the light was previously reflected causing the light to travel a longer distance
22
Q

What is the time dialation equation

A

n