Question

In flatness testing with interferometry, if surfaces are perfectly wrung. Then which option is correct regarding fringe pattern?

(a) No fringe pattern

(b) Fringes are closer

(c) Fringes are at great distance

(d) Indistinguishable pattern

I had been asked this question in an interview for internship.

This interesting question is from Interferometry Applied to Flatness Testing topic in section Measurement by Light-Wave Interference of Engineering Metrology

Answer 1

The correct option is (a) No fringe pattern

For explanation: If the surface between optical flat and work surface are perfectly wrung together then there will be no air gap between the surfaces and fringe pattern will be not observable.