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Refractive Index - IGCSE Physics Definition

Reviewed by: Ann Howell

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In IGCSE Physics, the refractive index, n, for the ratio of angles, is defined as the ratio of the sine of the angle of incidence and the sine of the angle of refraction of a wave in two different regions.

The refractive index for the ratio of angles is given by the equation:

n space equals space fraction numerator sin space i over denominator sin space r end fraction

Where:

  • n = the refractive index of the material

  • i = angle of incidence of the light (degree)

  • r = angle of refraction of the light (degree)

The refractive index, n, for the ratio of speeds, is defined as the ratio of the speeds of a wave in two different regions. It is given by the equation:

n space equals space fraction numerator speed space of space light space in space straight a space vacuum over denominator speed space of space light space in space straight a space material end fraction

The refractive index is a number that is always larger than 1 and is different for different materials. Objects which are more optically dense have a higher refractive index, e.g. n is about 2.4 for diamond. Objects which are less optically dense have a lower refractive index, e.g. n is about 1.5 for glass. Since the refractive index is a ratio, it has no units.

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Ann Howell

Reviewer: Ann Howell

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Ann obtained her Maths and Physics degree from the University of Bath before completing her PGCE in Science and Maths teaching. She spent ten years teaching Maths and Physics to wonderful students from all around the world whilst living in China, Ethiopia and Nepal. Now based in beautiful Devon she is thrilled to be creating awesome Physics resources to make Physics more accessible and understandable for all students, no matter their schooling or background.

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