Question

Which of the following is not true for glass scales?

(a) Graduations can be produced by depositing material

(b) Easily polished

(c) Able to work in case of reflected light but not in transmitting light

(d) Ordinary glass has 15-30% less thermal coefficient of expansion than steel

The question was asked during an interview.

Question is from Scales and Gratings topic in chapter Measurement by Light-Wave Interference of Engineering Metrology

Answer 1

Right option is (c) Able to work in case of reflected light but not in transmitting light

Easy explanation: Glass scales are stable, and are able to work in both transmitting and reflected light. Graduation on these scales can be produced by etching through ruled wax, by depositing material in the form of thin lines and by depositing photographic emulsions.