Paper 3 - Option Module - Turning Points - 3.12.3 - Special Relativity Flashcards
3.12.3 - Special relativity
3.12.3.1 - The Michelson-Morley experiment
What permeated the whole universe?
The ether.
What was the ether?
A substance that allowed the waves to travel, not getting in the way of rotating bodies.
What were Michelson and Morley trying to test in their experiment?
How much the ether slowed the speed of light.
What did Michelson and Morley use for their experiment?
An interferometer.
What did the interferometer allow?
The interference of light rays
Sketch a labelled diagram of the set-up of the interferometer.
In page 8.
What was the compensator used for the in the set-up?
Ensure that both beams travel through the same thickness of glass to prevent waves overlapping.
What was the equipment used for in the observation of the experiment?
- 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).
What was the expected result of the experiment?
Rotating apparatus through 90 degrees would swap beam directions relative to Earth’s absolute motion = fringe shift.
What was the actual result of the experiment?
Unable to detect fringe shift.
What was the conclusion to the Michelson and Morley experiment?
Ether does not exist.
Speed of light is invariant in free space - independent of the motion of source or observer.
What is a null result?
A result that does not support the hypothesis.
What is absolute motion?
The translation of a body from absolute place to another, but this is not true.
3.12.3.2 Einstein’s theory of special relativity
What is a frame of reference?
A set of coordinates used to determine positions and velocities of objects in that frame or stage.
What is an inertial frame of reference?
Those which move at constant velocity, not undergoing any acceleration or rotation, obeying Newton’s laws.
What is meant by the term postulate?
Assumption.
What are Einstein’s two postulates of special relativity?
- Speed of light in free space = invariant.
- Laws of physics have the same form in all inertial frames of reference.
3.12.3.3 Time dilation
What is proper time?
The amount of time that has passed, experienced by the stationary observer.
proper time = to.
State the time dilation equation.
Found in equation data sheet.
to > t.
Who measures the proper time, to, in the the time dilation equation?
Whoever is at both events (moving from A to B), is the person that measures proper time, to.
Explain how muons are evidence for time dilation and special relativity.
We observe that a muon takes longer than 2.2 microseconds to decay, giving its time to reach Earth’s surface.
3.12.3.4 Length Contraction
Define proper length.
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.
State the equation for length contraction.
Found in the data sheet.
lo > l.
What will remain constant in length contraction?
The width of the object, experiencing a change in length.
3.12.3.5 Mass and Energy
What is larger - the relativistic mass of a moving object, or its rest mass (mo)?
Relativistic mass.
What is the equation that links the relativistic mass to the rest mass of an object?
In page 10 of notes.
Sketch the graph of relativistic mass against speed.
In page 10 of notes.
How do you calculate total energy?
Total energy = KE + rest energy.
What is the equation that links total energy to proper/rest mass?
In page 11 of notes.
What is the equation for KE, given the total energy and rest mass?
In page 11 of notes.
Sketch a graph of KE against speed.
Page 20.
What was Bertozzi’s experiment?
To measure the speed of electrons with different kinetic energies.
How did Bertozzi measure the speed of electrons?
- 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.
How did Bertozzi accelerate the electrons?
Particle accelerator was used to emit the electrons at different/various KE.
How did Bertozzi calculate the KE of each electron?
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.
What relationship did Bertozzi find between the KE and speed of the electrons?
Values were very close to those predicted by Einstein’s theory of special relativity.
