THEORY OF THE DETERMINATION OF REFRACTIVE INDEX BY THE TOTAL INTERNAL REFLECTION METHOD

Abstract

The total internal reflection method is a standard method by which the refractive
index of the material of a prism and that of a liquid are determined in'
elementary physics laboratories. This method involves illumination of the matt
surface of a prism, mounted on a spectrometer table, with monocromatic light
and looking at one of the polished surfaces of the prism through the telescope
of the spectrometer. A line which separates a bright and a relatively dark
'region of the field of view can be observed when the experiment is carried
out and the angle corresponds to this line is measured by the circular scale
of the spectrometer. Using this result and the value of the angle of the prism,
the refractive index of the material of the prism can be calculated. The refractive
index of a liquid can be determined repeating the experiment after coating
one of the polished surfaces of the prism with a layer of the liquid. Procedure
of earring out this experiment is explained elaborately in many elementary text
books 1.2. However, the logical reasoning as spelt out in the derivation of
the theory does not satisfactorily answer all the questions that a student with
an inquiring mind might ask. This paper makes an attempt to rectify this
defficiency.