The reflection from cut diamond is much stronger than reflection from cut crystal (high refractive index lead glass) and which is again stronger than reflection from ordinary glass in air. Glass in water reflects very little but diamonds sparkle even under water.
The reflection/transmission ratio for non metals is governed by the Fresnel equations and must be calculated for each polarization (electric vector parallel and perpendicular to the surface) for angles of incidence that are not 90°.
For normal incidence the equations simplify (see the panel at right. The reflectance and transmittance add to one.
We have a means of measuring light intensity and polarizing filters. It would be possible to investigate some aspect of reflection and to compare data with calculations based on the fresnel equations but IB is not very enthusiastic about labs which merely test the validity of a formula. An enterprising idea would be needed.
Suggestions
1 If reflectance was measured the refractive index of a polished piece of opaque plastic could be found. Compare the reflectance (at near normal incidence from the top surface of clear, and colored, perspex sheets.
2 How does surface roughness affect measured reflectance, at normal incidence, and for other angles of incidence?