Physics 2102 Gabriela Gonz lez Michelson interferometers As we saw in the previous example interference is a spectacular way of measuring small distances like the thickness of a soap bubble since we are able to resolve distances of the order of the wavelength of the light for instance for yellow light we are talking about 0 5 of a millionth of a meter 500nm This has therefore technological applications In the Michelson interferometer light from a source at the left in the picture hits a semi plated mirror Half of it goes through to the right and half goes upwards The two halves are bounced back towards the half plated mirror interfere and the interference can be seen by the observer at the bottom The observer will see light if the two distances travelled d1 and d2 are equal and will see darkness if they differ by half a wavelength Einstein s messengers einsteinsmessengers org The largest Michelson interferometer in the world is in Livingston LA in LSU owned land it is operated by a project funded by the National Science Foundation run by Caltech and MIT and LSU collaborates in the project http www ligo la caltech edu Mirrors are suspended with wires and isolated from the ground motion The interferometer will detect ripples in the distance between the mirrors The LIGO project Hanford WA Hundreds of people working on the experiment and looking at the data LIGO Scientific Collaboration www ligo org Livingston LA http www amnh org sciencebulletins sid a f gravity 20041101 src l American Museum of Natural History Science Bulletins Gravity Making Waves Young s double slit experiment Young s double slit experiment Path difference L d sin Bright fringe L m d sin Dark fringe L m 1 2 d sin The intensity on the screen is I I0 4cos2 2 with 2 d sin Bright fringe L m d sin Dark fringe L m 1 2 d sin I I0 4cos2 2 with 2 d sin Does the spacing between fringes in a two slit interference pattern increase decrease or stay the same if a the slit separation is increased b the color of the light is switched from red to blue and c the whole apparatus is submerged in cooking sherry d If the slits are illuminated with white light then at any side maximum does the blue component or the red component peak closer to the central maximum Bright fringe L m d sin Dark fringe L m 1 2 d sin I I0 4cos2 2 with 2 d sin In a double slit experiment the fourth order maximum for a wavelength of 450 nm occurs at an angle of 90 Thus it is on the verge of being eliminated from the pattern because cannot exceed 90 in Eq 35 14 a What range of wavelengths in the visible range 400 nm to 700 nm are not present in the third order maxima To eliminate all of the visible light in the fourth order maximum b should the slit separation be increased or decreased and c what least change in separation is needed
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