Refractometer - Refractometer

Japanese: 屈折計 - くっせつけい

$Refractometer - Refractometer$

An instrument that measures the refractive index of a medium (material) for light. When two different media meet at a plane, the light passing through the interface is refracted, and the angles θ ₁ and θ ₂ between the normal to the interface and the light ray always satisfy the following relationship:

n ₁ sinθ ₁ ＝ n ₂ sinθ ₂
where n1 _and n2 are the refractive indices of the respective media. Using this relationship, the refractive index of a substance can be calculated based on the standard that defines the refractive index of a vacuum as 1. If the substance in question is a solid, _a prism is made with it and _θ1 and _θ2 are measured. If the substance in question is a liquid, an effective method is to detect the critical angle, that is, _θ2 when _θ1 becomes a right angle, by using the phenomenon of total reflection (Abbe refractometer).

Another means of determining the refractive index is to measure the wavelength of light in the medium, using a type of optical interferometer.

[Mitsui Kiyoto]

[Reference] | Interferometer | Refractive index | Refractive index

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

光の媒体（物質）の光に対する屈折率を測定する計器。二つの異なる媒体が平面を境として接しているとき、この境界面を通過する光線は屈折し、境界面の法線と光線との角度θ₁、θ₂はつねに次の関係を満たす。

　　n₁sinθ₁＝n₂sinθ₂
n₁、n₂はそれぞれの媒体の屈折率である。この関係を用い、真空の屈折率を1と定める基準に基づいて物質の屈折率が求められる。対象物質が固体の場合には、これでプリズムをつくりθ₁およびθ₂を測定する。対象物質が液体の場合には、臨界角、すなわちθ₁が直角となるときのθ₂を全反射現象によって検出する方法が効果的である（アッベ屈折計）。