Question

Which of the following is not true for optical flats used in surface contour test?

(a) Colourless

(b) Always wrung on the work piece

(c) Work piece and optical flat should be free from dust, dust and fingerprints

(d) Optical flat should always be lifted from work piece

The question was posed to me in an interview for internship.

My question comes from Surface Contour Test in chapter Measurement by Light-Wave Interference of Engineering Metrology

Answer 1

The correct answer is (b) Always wrung on the work piece

To elaborate: Optical flats should never be wrung on surface to be measured because it scratches too readily. Optical flats should be rested on work piece carefully. It should be clean and free from dust.