Determination of the refractive index of a glass prism

Refraction is the change in direction of a wave due to a change in speed at the boundary between two media of different density. The Latin word “fract” in refraction means to break. Refraction is the “breaking or bending” of waves as it travels to a different density media. The absolute index of refraction of a material is defined as the ratio of the speed of light in a vacuum (c) with respect to the speed of light in the material (v). From this definition, we see that the index of refraction is a dimensionless number that is greater than one because c is always greater than v.

The index of refraction varies with frequency or color. Frequency does not change as light travels from one medium to another. Since frequency remains unchanged, the change in the speed of light in the material is directly proportional to the change in the wavelength of light as it travels from one medium to another.

The name crown glass comes from the manufacturing process. But, it actually is a type soda-lime glass, which is one of the most common glass made on earth. Crown glass that were made into windows were made by blowing glass into a hollow tube. As the tube and the flat disk is spun, it spins out a crown shaped piece of glass where it forms at the bottom of the hollow tube. Crown glass is also used for optical glasses that are used in compound lenses. It has a lower refractive index and less dispersion than flint glass, but is more durable.