A-Level Physics AQA 7408

The Michelson-Morley experiment

Principle of the Michelson-Morley interferometer.

Outline of the experiment as a means of detecting absolute motion.

Significance of the failure to detect absolute motion.

The invariance of the speed of light.

Einstein’s theory of special relativity

The concept of an inertial frame of reference.

The two postulates of Einstein’s theory of special relativity:

1. physical laws have the same form in all inertial frames
2. the speed of light in free space is invariant.

Time dilation

Proper time and time dilation as a consequence of special relativity.

Time dilation: $t = \dfrac{t_0}{\sqrt{1-\dfrac{v_2}{c_2}}}$

Evidence for time dilation from muon decay.

Length contraction

Length of an object having a speed v

$l = l_0\sqrt{1 - \dfrac{v_2}{c_2}}$

Mass and energy

Equivalence of mass and energy,

$E = mc^2$; $E = \dfrac{m_0c^2}{\sqrt{1-\dfrac{v_2}{c_2}}}$

Graphs of variation of mass and kinetic energy with speed.

Bertozzi’s experiment as direct evidence for the variation of kinetic energy with speed.