How does a Michelson interferometer split the incoming light?
A partially reflecting beam splitter divides it into two beams travelling along perpendicular arms.
AQA A-level Physics (7408) · 3.12.3.1
Revise AQA A-level Physics (7408) specification point 3.12.3.1, The Michelson-Morley experiment (A-level only), with free active-recall flashcards. Flip through the set or review every question and answer below.
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How does a Michelson interferometer split the incoming light?
A partially reflecting beam splitter divides it into two beams travelling along perpendicular arms.
How do the two beams in a Michelson interferometer recombine?
Mirrors reflect them back to the beam splitter, where they recombine and interfere.
What aspect of the beams' travel affects their phase difference in a Michelson interferometer?
Their relative travel times.
How does the phase difference between the returning beams affect a Michelson interferometer's fringe pattern?
It determines the pattern; a change in phase difference can shift the fringes.
What motion was the Michelson–Morley experiment designed to detect?
Earth’s motion relative to a hypothesised stationary luminiferous ether.
Why would rotating the Michelson–Morley interferometer produce a fringe shift if ether motion affected its perpendicular arms differently?
Rotation would change the relative light travel times along the arms, shifting the interference fringes.
What fringe shift did the Michelson–Morley experiment detect?
No fringe shift of the expected size was detected.
What idea about light did the Michelson–Morley null result challenge?
The idea that light requires a stationary ether as its medium.
How does the Michelson–Morley result relate to the invariance of the speed of light?
It is consistent with invariance, but does not by itself establish the principle in full.
What does the invariance of the speed of light in a vacuum state?
It has the same value in every inertial reference frame, regardless of the motion of the source or inertial observer.
What is the approximate speed of light in a vacuum?
What status does the invariance of the speed of light have in special relativity?
It is a postulate of special relativity.
What is the classical expectation about how the relative motion of source and observer affects measured speeds?
Measured speeds depend on their relative motion.