A-Level Physics Specification

AQA 7408

Section 12.3: Special relativity

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#12.3.1

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.

#12.3.2

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.

#12.3.3

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.

#12.3.4

Length contraction

Length of an object having a speed v

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

#12.3.5

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.