Question

Which of the following is the incorrect condition for a perfectly flat surface when tested for interferometry?

(a) Monochromatic light is used

(b) Viewing angle should be greater than 0^o

(c) Optical flats are important in light wave measurement

(d) For perfect flat surface alternate light and dark bands are observed

I got this question in an interview for internship.

My question is based upon Interferometry Applied to Flatness Testing in chapter Measurement by Light-Wave Interference of Engineering Metrology

Answer 1

Right option is (c) Optical flats are important in light wave measurement

Best explanation: Angle at which bands are viewed is called viewing angle. Viewing angle should be 0^o that is line of sight should be at 90 degrees to the reference surface of optical flats. As this angle increases it will cause error.