homework and exercises - Determining the refractive index of a foil

(59th Polish Olympiad in Physics, final stage, experimental part, 2010)

You have at your disposal:

• a sample of blue foil of a homogeneous material, placed between two glass panes in a slide frame


• a laser pointer


• a meter of the power of light composed from a photodiode, a battery and a voltmeter whose readings are proportional to the power of light falling on the active surface of the photodiode


• graph paper


• two wooden blocks



• adhesive tape

Determine the refractive index of the material the blue foil is made of for the laser wavelength of light.

Note 1: The thickness of the foil is approximately 0.1 mm and the thickness of the glass panes on its both sides is approximately 1 mm. Between the panes and foil there is a very thin layer of a liquid, which has a refractive index very close to the refractive index of glass.

Note 2: The frame is not shut completely - it should not be pressed or opened. Make sure not to smear the surface of the panes.

There is no official solution available for this problem. How could it be solved?