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5. An analyzer oriented to allow minimum flux has its transmission axis perpendicular to the major axis of the ellipse of the polarized light and light proportional to the minor axis is transmitted. Any detector placed behind the analyzer has a threshold intensity and light more than the threshold value should fall on the detector to indicate the departure from null. In other words, for a light source of given intensity, light of a definite ellipticity should incident on the analyzer to indicate a departure from null. This ellipticity has been defined as the threshold ellipticity of the detector for a given light intensity.