Turning Points- Special Relativity Flashcards
What is the ether?
A substance that was believed to fill all space and be responsible for light propagation
What is ether drift?
A theory that the Earth’s ether carried light along with it. This implied that light should travel faster when travelling in the direction of the ether, however
was later proved to be false.
What is absolute motion?
The idea that everything moves relative to the ether
What is the Michelson-Morley experiment set up?
An interferometer which consists of a monochromatic light source, a half-silvered mirror which splits the beam, a glass block, two mirrors same distance from beam splitter and a viewing telescope
What was the aim of the Michelson-Morley experiment?
To measure the absolute speed of the Earth through the ether. They believed the speed of light parallel to Earth’s motion would be affected and light perpendicular would be unaffected, so rotating the apparatus would shift the interference pattern
What was the result of the Michelson-Morley experiment?
When the interferometer was rotated, there was no shift in interference pattern which was not expected, showing time taken for light to travel was unaffected by rotation of apparatus
What was drawn from the results of the Michelson-Morley experiment?
-Ether doesn’t exist or Earth drags it along as it moves
-Speed of light is invariant in free space, independent of the motion of the source or observer
Why was a half-silvered mirror and glass block used in the Michelson-Morley experiment?
-Half-silvered mirror reflects some light, allows some to pass through creating two perpendicular light beams
-Glass block, compensating plate, used so both beams pass through same amount of glass
What is an inertial frame of reference?
A frame of reference which is not accelerating. Two inertial frames of reference travel at a constant velocity relative to each other.
What were Einstein’s two postulates?
1) The laws of physics are the same in all inertial frames of reference
2) The speed of light in free space is invariant (independent of motion of source or observer)
What is time dilation?
A consequence of special relativity that means time appears to move slowly when an object is moving
What is a stationary observer?
An observer stationary relative to the frame of reference where an event is occurring
What is an external observer?
An observer outside the frame of reference where an event is occurring and so has a non-zero constant velocity relative to it
What is proper time, t o ?
The amount of time passed experienced by the stationary observer, in the frame of reference where the event is occurring
What is v in gamma?
The velocity at which the ‘stationary observer’ is travelling (for the external observer)
What is always true for proper time t o and time measured by an external observer?
Proper time t o will always be less than the time measured by the external observer as the denominator is always less than 1.
How does muon decay give experimental evidence for time dilation?
Muons enter upper atmosphere at relativistic speeds and are expected to decay before reaching the ground but are detected as time dilates for them and so seems to move slower for them, so fewer half-lives pass so fewer decay and more are detected.
What is length contraction?
A consequence of special relativity that causes the length of objects moving at high speeds to appear shorter to an external observer
What is the proper length l o?
The length of an object as measured by an observer stationary relative to the object
How does muon decay provide experimental evidence for length contraction?
Muons enter upper atmosphere at relativistic speeds and are expected to decay before reaching the ground but are detected as length contracts for them so they are able to reach the ground
How are mass and energy related?
Object at rest: E = mc^2
How does mass change as an objects speed increases?
Transferring energy to an object causes its mass to decrease so the faster an object travels, the greater its mass becomes. Relativistic mass m is m = γm o
What does the graph of relativistic mass against speed look like?
Starts at m o on y axis, almost horizontal line until around 0.8c then starts increasing exponentially with asymptote at c
What does the graph of kinetic energy against speed look like?
Starts at origin, almost horizontal line until around 0.6c where starts increasing exponentially with asymptote at c
When does the normal equation for Ek apply?
When objects are moving below relativistic speeds (1/10th the speed of light)
What is total energy equal to?
Etotal = Ek + Eo
total energy= kinetic energy + rest energy
What is relativistic energy?
When an object approaches relativistic speeds, the mass will increase, resulting in an increase of energy known as relativistic energy
What was Bertozzi’s experiment set-up?
A particle accelerator, two detectors, an oscilloscope, aluminium plate connected to temperature sensor
How did Bertozzi’s experiment work?
-Electrons released in pulses from particle accelerator which could emit electrons at varying Ek
-Pass detectors A and B with known distance between them, time taken calculated using oscilloscope’s time base and peaks
-Electrons collide with plate transferring Ek to heat measured by temp. sensor, individual energies calculated using number of electrons
What were the results from Bertozzi’s experiment?
Bertozzi plotted his results of Ek against speed and found the graph was very similar to that predicted by Einstein’s theory of special relativity, supporting it
Why can an object not reach the speed of light?
According to special relativity, as an object’s speed approaches c, its mass approaches infinity and so its energy does too which is impossible
