Why the mirrors are placed perpendicular to each other in Michelson's interferometer?

Answer 1

It is used to bounce the light beams. There is a seismograph that works on the same principle and thus is immediately responsive to earthquake jolts. There are two beams at an L- shaped angle- yes it could be called perpendicular or Right angles. the light beam goes between them, comes the quake- well the apparatus will shake and record any beam displacement- this applies to the Seismograph, not the other application, but they are similar.