Refractive Index (Index Of Refraction) | Nikon's MicroscopyU

Where n represents the refractive indices of material 1 and material 2 and θ are the angles of light traveling through these materials with respect to the normal. There are several important points that can be drawn from this equation. When n(1) is greater than n(2), the angle of refraction is always larger than the angle of incidence. Alternatively when n(2) is greater than n(1) the angle of refraction is always smaller than the angle of incidence. When the two refractive indices are equal (n(1) = n(2)), then the light is passed through without refraction.

In optical microscopy, refractive index is an important variable in calculating numerical aperture, which is a measure of the light-gathering and resolving power of an objective. In most instances, the imaging medium for microscopy is air, but high-magnification objectives often employ oil or a similar liquid between the objective front lens and the specimen to improve resolution. The numerical aperture equation is given by:

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