Special Relativity Flashcards
(14 cards)
What was the goal of the Michelson-Morley experiment?
To detect Earth’s motion through the hypothesised aether by measuring changes in the speed of light due to Earth’s motion.
What setup did Michelson and Morley use?
An interferometer that split a light beam into two perpendicular paths, reflected them back, and recombined them to observe interference patterns.
What result did Michelson-Morley observe?
No shift in the interference pattern, no matter how the device was rotated—contradicting the aether theory.
What did the null result imply?
That the speed of light is the same in all directions—light does not need a medium, and absolute motion can’t be detected.
What are the two postulates of special relativity?
The laws of physics are the same in all inertial frames.
The speed of light in a vacuum is constant for all observers.
What is time dilation?
Moving clocks appear to run slower.
T= T0 / √(1 - v²/c²) where T0 is proper time (in the rest frame), and T is observed time.
What is the Lorentz factor γ?
γ = 1 / √(1 - v²/c²)
Used in time dilation, length contraction, and relativistic mass calculations.
What is length contraction?
Moving objects appear shorter in the direction of motion:
L = L0 / γ
Where L0 is proper length (at rest).
What is relativistic mass?
An object’s mass increases with speed:
m = γm0
What happens to the kinetic energy of a relativistic particle?
E_k = (γ - 1)m0c²
Why can’t 1/2 mv² be used at relativistic speeds?
Because mass increases with speed and energy transfer becomes non-linear; relativistic equations must be used.
What is total energy in special relativity?
E_total = γm0c²
Includes rest and kinetic energy.
How can you calculate the required accelerating PD for a relativistic electron?
Use E_k = eV with relativistic E_k = (γ - 1)m0c², not classical 1/2 mv².
How do muons support time dilation?
Muons have a short half-life, but are observed to travel farther than expected on Earth due to time dilation in our frame and length contraction in theirs.
