How does continuous wedge filter differ from normal interference

how-does-continuous-wedge-filter-differ-from-normal-interference

How does continuous wedge filter differ from normal interference filter used in absorption spectroscopy?

A. It permits continuous selection of different wavelength

B. It allows a narrow band of wavelengths to pass

C. It has two semi-transparent layers of silver

D. Space layer is made of a substance having low refractive index

This question was posed to me in exam.

This interesting question is from Absorption Instrumentation and Block Diagram Representation in section Colorimetry and Spectrometry of Analytical Instrumentation

The correct choice is A. It permits continuous selection of different wavelength

For explanation: It allows continuous selection of wavelength by using a spacer film of graded thickness. Rest of the options are properties of normal interference filters.