Question

To measure the tiny motion of one tectonic plate relative to another, seismologists in Iceland have set up the following interferometer-like device: A laser source producing laser light with wavelength 500 nm is set up on one side of a chasm that forms the boundary between two tectonic plates. The light is split into two beams using an angled piece of glass (acting as a "beam splitter"). One part of the beam crosses the chasm and is reflected back by a mirror on the far side. The other part of the beam bounces between mirrors all on the same side as the source. The beams are then recombined via the beam splitter and picked up by a detector. The setup is shown below. Note that all light is the same color, but here blue and green have been used to show the two different paths that the light takes. Mirror Chasm Laser Mirror Beam Splitter Detector North American Plate Eurasian Plate It is observed that over the course of a day the detector alternates between detecting little light and lots of light 400 times. What is the speed with which the tectonic plates are moving apart? Hints: • You don't know the actual path length of either arm of this interferometer. But all you need to figure out is how quickly the path length difference changes, and only the horizontal arm across the chasm changes its length. • By how much does the arm across the chasm have to get longer so that the detector goes from picking up light to picking up dark to picking up light again?

Answer 1

1 0.25 25 X102 frequency of 10²4 T yo sooom (wavelengths) V 9 m *10 v= f (formula) Speed v=0.25 X 10t2y 5 op -25 x 5Jx10=12+ u-(195) x 10-19 m ser V = 1.25 810 Bee See tom CSscanned with CamScanner