. Light, a textbook for students who have had one year of physics. rmining wavelengths. It is moreaccurate than a grating for this purpose. The technique of itsuse, however, is somewhat involved. 82. Interference in white light.—In any interference ex-periment, it is found to be impossible to observe interference 164 LKJI IT fringes if white, or composite, light is used, except when thedifference in path amounts to only a few wavelengths. In mostexperiments, matters are so arranged that in part of the fieldof view the difference in path of the interfering rays is zeroor nearly zero, while in o
. Light, a textbook for students who have had one year of physics. rmining wavelengths. It is moreaccurate than a grating for this purpose. The technique of itsuse, however, is somewhat involved. 82. Interference in white light.—In any interference ex-periment, it is found to be impossible to observe interference 164 LKJI IT fringes if white, or composite, light is used, except when thedifference in path amounts to only a few wavelengths. In mostexperiments, matters are so arranged that in part of the fieldof view the difference in path of the interfering rays is zeroor nearly zero, while in other parts it may be many wave-lengths; but in some, as with a thin film whose thickness isuniform but amounts everywhere to say more than six or eightwavelengths, the difference in path is always relatively cases of the latter sort, fringes are absolutely invisible withwhite light, though they may be very clear with monochromaticlight. In cases of the former sort, white light shows a fewfringes, usually not more than ten or a dozen, where the differ-. Figure 84 ence in path is quite small, but none whatever in the rest ofthe field. Consider, for example, Newtons rings. Here thethickness of the air-film ranges from zero, where the lens andthe flat disc come into contact, to larger and larger values aswe recede from that point. Figure 84B is a photograph of therings when the lighl comes from a tungsten filament ! is therefore composite white light. Tt does not reproducethe visual appearance quite faithfully, because the range ofwavelengths for photographic sensitivity is somewhat differentfrom that for visual sensitivity, but the general character is INTERFERENCE IN WHITE LIGHT 165 the same. 84A, on the other hand, is taken with monochroma-tic light, and the difference is striking. In the original photo-graph, fine clear rings may be counted clear out to the edgesof the disc in 84A, while in 84B only a few can be seen. Theselast of course were brilliantly colo
Size: 2136px × 1170px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectlight, bookyear1921
