. A text book of physics, for the use of students of science and engineering . Fig. 526.—Apparent raising by transparentmedium. Substance. Alcohol < li own glasa (moan)Diamond -Flint glass (mean) 1 -361 -512-421 65 Substance. Glycerine-Tee - TurpentineWater 1-471 -311-471 333 Those values of // are for the sodium D lino, for light travelling fromair to the substance at 15° C. XLV REFRACTIVE INDEX 579 Passage of a ray from water to glass.—In the preceding pages thepassage of a ray from air to a medium such as water or glass has beendealt with. When the ray passesfrom one transparent medium t
. A text book of physics, for the use of students of science and engineering . Fig. 526.—Apparent raising by transparentmedium. Substance. Alcohol < li own glasa (moan)Diamond -Flint glass (mean) 1 -361 -512-421 65 Substance. Glycerine-Tee - TurpentineWater 1-471 -311-471 333 Those values of // are for the sodium D lino, for light travelling fromair to the substance at 15° C. XLV REFRACTIVE INDEX 579 Passage of a ray from water to glass.—In the preceding pages thepassage of a ray from air to a medium such as water or glass has beendealt with. When the ray passesfrom one transparent medium toanother, the index of refractionmay be found as follows. Letthe index of refraction for a raypassing from air to, say, waterbe and from air to, say, glassbe fj-2. Consider the ray ABCDpassing from air, through a layerof water with parallel faces, andinto glass (Fig. 527). At the first surface, sin isin r = HV. Fig. -Index of refraction for any twomedia. For a ray passing from air toglass, sin i/sm r = /x2, the parallellayer of water between them not producing any deviation (seeExpt, 123). sin i sin r fi„ But sin r sin %sin rsin r -i- ? ?-*Pi >1 sin isin r from water to and this is the index of refraction of a ray travellinglass. x , , , , Index for air and glass \< Hence, Index for water and glass =,—3 j = 3 1— 0 Index for air and water Glass and water have been chosen as examples, but the rule applieswhatever the substances may be. Visibility of transparent bodies.—Reflection only occurs when there 1is a discontinuity of refractive index, such as occurs at the surface offseparation of two media. If the two media have the same refractiveindex, no reflection occurs at their surface of separation. Thuscedar-wood oil has very nearly the same refractive index as glass,and fragments of glass immersed in it cannot be seen, as there isthen no reflection at the surfaces of the
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