Question

For checking straightness, straight edge is placed over a surface and these two are viewed against the light. Which of the following option true if colour of light is red?

(a) Gap between 0.12 to 0.17 mm

(b) Gap between 0.2 to 0.7 mm

(c) Gap between 1.7 to 2 mm

(d) Gap between 0.0012 to 0.0017 mm

The question was asked in final exam.

I need to ask this question from Straightness topic in division Straightness, Flatness, Squareness, Parallelism, Circularity and Rotation of Engineering Metrology

Answer 1

Right choice is (d) Gap between 0.0012 to 0.0017 mm

To elaborate: Straight edge and surface are viewed against the light. The gap between surface and straight edge should be negligible small for perfect straight surfaces and the measurement of straightness is observed by seeing the colour of light produced due to interference caused by diffraction of light.