Special relativity Flashcards
What is the ether?
fixed object that everything must move relative to
(what move absolute motion relative to, medium for light waves)
What is the Michelson-Morley experiment?
tried to find absolute speed of Earth using an interferometer.
- used 2 mirrors + a partial reflector to send a beam of light in 2 perpendicular directions.
- These beams are reflected back + recombined to form an interference pattern.
Based on the shift in interference patterns when the experiment is run in different orientations, the speed of the Earth should have been calculated.
Results from Michelson-Morley experiment?
They repeated experiment, but could never find any results from their interference patterns.
So concluded that:
Absolute motion is impossible to detect.
The speed of light is equal for all observers.
State Einstein’s 2 postulates of theory of special relativity
- Physical laws have the same form in all inertial frames - so experiments will have same result in any inertial frame of reference.
- speed of light in free space is invariant - c will not change if observer or source is moving.
What is an inertial frame?
frame is one in which objects will not accelerate if they are left untouched by external forces (Newton’s first law).
What is time dilation?
Time is different at different velocities within an inertial frame of reference.
As velocity increases + approaches the speed of light, time will run slower
What is the Lorentz factor?
factor by which time dilates
- determines how much time will differ.
What proof do we have of time dilation?
muon decay:
- Muons have a very short half-life + should decay before they get through atmosphere.
BUT muons are still detected on surface of Earth.
This is because muons travel so quickly, that time dilation provides them w more time to move.
Condition for time dilation?
must be in an inertial frame of reference
What is length contraction?
As objects move faster in an inertial frame of reference, they will become shorter.
What happens to mass as velocity changes?
as an object gains velocity it also gains mass in an inertial frame of reference.
E=mc^2 - shows that mass + energy are equivalent?
What is Bertozzi’s Experiment?
sought to provide experimental proof that mass increases with velocity
What was method for Bertozzi’s Experiment?
- used linear particle accelerators to accelerate electrons into an aluminium disc.
- recorded time taken for electrons to reach disc, along with energy provided to electron.
- used heat generated on aluminium disc to calculate final velocity of the electrons.
- did this by equating heat and kinetic energy.
Results from Bertozzi’s Experiment?
Found that velocities of electrons did not continue to increase as supplied more energy to electrons.
BUT approached a max value of c
This is first evidence of special relativity.
Evidence of relativistic mass?
accelerating e- to high speeds
measured specific Q
confirmed change in mass
