How do you perform an experiment to find the refractive index of a glass block?

Answer 1

To find the refractive index of a glass block for a particular wavelength of light, shine a beam of light of that wavelength through a material for which the refractive index n1 is known onto the glass block such that the angle between the beam and the block's surface θ1 is between zero and 90 degrees. Measure the angle between the part of the beam that enters the block and the block's surface θ2 and use Snell's law:

n2 = n1 cos(θ1) / cos(θ2).


Note: Typically Snell's law is expressed in terms of the angle between the beam and the direction normal to the interface and there for sines are used instead of cosines, but the use of cosines allowed the question to be answered without assuming knowledge of the concept "normal" to the interface.

Answer 2

1. Set up a ray box and a glass block on a sheet of paper.
2. Shine a ray of light through the glass block and observe the incident and refracted rays.
3. Measure the angles of incidence and refraction, then use Snell's Law (n1sinθ1 = n2sinθ2) to calculate the refractive index of the glass block.