Question

Which of the following option is incorrect for flatness testing by interferometry?

(a) For checking concave or convex surface optical flat is pressed lightly

(b) If angle between optical flat and work surface reduces, then fringe spacing decreases

(c) For perfectly flat surface condition of complete interference satisfies

(d) Only one point contact between optical flat and surface is possible in some cases

This question was addressed to me in an interview for job.

I would like to ask this question from Interferometry Applied to Flatness Testing in division Measurement by Light-Wave Interference of Engineering Metrology

Answer 1

The correct option is (b) If angle between optical flat and work surface reduces, then fringe spacing decreases

Best explanation: If ‘θ’ that is the angle between optical flat and work surface whose flatness to be measured reduces then the fringe space increases and if ‘θ’ increases then fringes brought more closer that is fringe spacing decreases.