i) The interferometer set-up is modified such that the length of BC is 0.000525 mm longer than the length of AC. Explain what effect this change will have on what you observe on the screen.
An interferometer is an instrument that uses interference effects to make
very precise measurements of small changes in distance.
Figure QB3a shows the set-up of a simple interferometer. The light
produced by the laser (λ = 700 nm) travels to the beam splitter, C (a halfsilvered mirror), where 50% of the laser light travels straight through
without changing direction (beam 1) and the other 50% is reflected
(beam 2).
Beam 1 hits mirror A and returns to the beam splitter, where it is then
reflected towards the screen (D). Beam 2 hits mirror B and returns to
the beam splitter, where it then travels straight through without changing
direction, also reaching the screen.
All parts of the interferometer are suitably enclosed such that the only
light inside the device comes from the laser.
(i) Assuming that AC and BC are the same length, explain what you
would expect to observe on the screen and why.
(ii) The interferometer set-up is modified such that the length of BC
is 0.000525 mm longer than the length of AC. Explain what effect
this change will have on what you observe on the screen.
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