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 half- silvered 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) (ii) Assuming that AC and BC are the same length, explain what you would expect to observe on the screen and why. 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 half- silvered 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) (ii) Assuming that AC and BC are the same length, explain what you would expect to observe on the screen and why. 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.