Definition
The refractive index (n) is a measure of how much light is bent, or refracted, when it enters a substance.
It is defined as the ratio of the speed of light in a vacuum to the speed of light in the material:
where:
c is the speed of light in a vacuum.
v is the speed of light in the material.
Determination
The refractive index can be determined using several methods:
Abbe Refractometer: A common instrument where a sample is placed between two prisms, and the angle of refraction is measured.
Critical Angle Method: Involves measuring the critical angle at which light is totally internally reflected.
Dispersion Method: Measures refractive index across different wavelengths to study dispersion.
Properties:
Snell’s Law:
The refractive index determines how light bends when entering a different medium. Snell's Law states:
where n1 and n2 are the refractive indices of the two media, are the angles of incidence and refraction, respectively.
Applications of Refractive Index:
Optics: Design of lenses, prisms, and optical fibers.
Quality Control: Checking the purity of substances.
Medical Diagnostics: Determining the composition of biological samples.