Efek Sagnac: Perbedaan antara revisi
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[[File:sagnac interferometer.png|frame|right|Gambar 1. Diagram skematik suatu interferometer Sagnac interferometer.]]
'''Efek Sagnac''' ({{lang-en|Sagnac effect}}, juga disebut "Interferensi Sagnac"), adalah suatu gejala yang dijumpai dalam [[interferometri]] yang ditimbulkan oleh [[rotasi]]. Dinamai menurut penemunya, seorang ahli Fisika dari Perancis, [[Georges Sagnac]]. Efek Sagnac muncul dengan sendirinya dalam suatu sistem yang disebut "Interferometer cincin" ("''ring interferometer''"). Suatu berkas cahaya dipisah menjadi dua dan kedua berkas hasilnya dibuat melalui jalur yang sama dengan arah berbalikan. Untuk membentuk suatu "cincin" jalur trajektori itu harus melingkupi suatu area. Pada waktu kembali ke titik awal kedua berkas cahaya itu diizinkan keluar dari cincin dan mengalami "Interferensi gelombang cahaya". Fase relatif dari kedua berkas yang keluar ini, dan juga posisi dari tepi-tepi/''fringe'' interferensi, digeser sesuai kecepatan angular ("''angular velocity''") peralatan itu. Sistem ini juga disebut "'''interferometer Sagnac'''". Efek Sagnac ini diterapkan sehari-hari dalam [[giroskop]] laser dan giroskop ''fiber optic'', serta [[GPS|sistem pemosisi global (GPS)]].
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A [[gimbal]] mounted mechanical [[gyroscope]] remains pointing in the same direction after spinning up, and thus can be used as a rotational reference for an [[inertial navigation system]]. With the development of so-called [[laser gyroscope]]s and [[fiber optic gyroscope]]s based on the Sagnac effect, the bulky [[Inertial navigation system#Gimballed gyrostabilized platforms|mechanical gyroscope]] is replaced by one having no moving parts in many modern inertial navigation systems.
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|journal=Comptes Rendus
|volume=157
|pages=1410–1413}}</ref>
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In 1926, an ambitious ring interferometry experiment was set up by [[Albert Abraham Michelson|Albert Michelson]] and [[Henry Gale (astrophysicist)|Henry Gale]]. The aim was to find out whether the rotation of the Earth has an effect on the propagation of light in the vicinity of the Earth. The [[Michelson–Gale–Pearson experiment]] was a very large ring interferometer, (a perimeter of 1.9 kilometer), large enough to detect the angular velocity of the Earth. The outcome of the experiment was that the angular velocity of the Earth as measured by astronomy was confirmed to within measuring accuracy. The ring interferometer of the Michelson-Gale experiment was not calibrated by comparison with an outside reference (which was not possible, because the setup was fixed to the Earth). From its design it could be deduced where the central interference fringe ought to be if there would be zero shift. The measured shift was 230 parts in 1000, with an accuracy of 5 parts in 1000. The predicted shift was 237 parts in 1000.<ref>Albert Abraham Michelson, Henry G. Gale: ''[http://adsabs.harvard.edu/abs/1925ApJ....61..140M The Effect of the Earth's Rotation on the Velocity of Light]'', in: ''The Astrophysical Journal'' 61 (1925), S. 140–145</ref>
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