This set of Engineering Metrology Multiple Choice Questions & Answers (MCQs) focuses on “Methods of Measuring Surface Finish”.
1. Which of the following is the best for the examination of surface finish?
a) Touch inspection
b) Visual inspection
c) Scratch inspection
d) Microscopic inspection
Explanation: Microscopic inspection is the best method for examining the surface finish. Visual, touch and scratch inspection methods are not as accurate as microscopic. In these methods, minute flaws can’t be detected.
2. Upto which limits irregularities can be detected with touch inspection of a surface?
a) 0.0001 mm
b) 0.001 mm
c) 0.01 mm
d) 0.1 mm
Explanation: Touch inspection method can tell which surface is rougher. In this method, the finger-tip is moved along the surface at a speed of about 25/sec and the irregularities of about 0.01 mm can be easily detected.
3. Which of the following material is not used for rubbing on the surface to be inspected in scratch inspection?
a) Softer material
b) Hard material
d) Lead babbitt
Explanation: In scratch inspection method, a softer material like plastic or lead babbitt is rubbed over the surface to be inspected. It carries the impression of the scratches on it which can be easily visualised.
4. Which of the following option is true for given statements about method of measurement of surface finish?
Statement 1: Minute flaws can be easily detected by touch inspection.
Statement 2: Direct instrument measurement is enabled to determine a numerical value of surface finish.
a) F, T
b) T, F
c) F, F
d) T, T
Explanation: The main limitation of the method of inspection by touch is that the degree of surface roughness can not be assessed by this and also the minute flaws can’t be detected by the only touch.
5. What is the limitation of microscopic inspection to check surface finish?
a) An average value is needed
b) Small portion of surface can be detected at a time
c) A master finish surface is also needed
d) It is necessary to inspect whole surface together
Explanation: Microscopic inspection method have some limitation that at a time only a small portion of the surface can be inspected. So for inspection, several readings are required in this method to get an average value.
6. In the method of microscopic inspection what is the angle of beam light with the work?
Explanation: In one method of microscopic inspection, a straight edge is placed on the surface to be inspected and a beam of light is projected at about 60 degree to the work. The shadows cast into the surface scratches are magnified and studied.
7. Which of the following is true for a method of measurement of surface finish with surface photographs?
a) Different type of illumination is needed
b) No effect of type of illumination
c) Same type of illumination is needed
d) Monochromatic light is needed
Explanation: In the method of surface inspection with magnified photographs of the surface are taken with different types of illumination. After this photographs with different illumination are studied and compared.
8. In case of vertical illumination in measuring surface finish with surface photographs, which will appear as bright area?
a) Flat portion
Explanation: In the inspection of surface with photographs if we use vertical illumination, then irregularities and scratches appear as dark spots and flat portion of the surface as bright area. But in case of oblique illumination, the case is reverse.
9. Which of the following method use pendulum in measuring the surface finish?
a) Micro interferometer
b) Wallace surface dynamometer
c) Reflected light intensity method
d) Microscopic inspection
Explanation: Wallace surface dynamo meter is like a friction meter which consists a pendulum in which the testing shoes are present which are clamped to a bearing surface and a spring pressure which is predetermined can be applied.
10. Which of the following is not true for the method of measurement of surface finish by micro interferometer?
a) Optical flat is used
b) Monochromatic source of light is used
c) Depth of defect can’t be measured
d) Interference lines plays an important role in identification of the defect
Explanation: In the method of inspection of surface by using micro interferometer, an optical flat is used which is placed on the surface to be examined and illuminated by using monochromatic light. Interference bands are studied by using a microscope. Defects or scratches appear as interference lines extending from the dark bands into the bright bands.
11. Which of the following is the direct measure of surface finish in Wallace surface dynamometer?
a) Time of swing
b) Angle of swing
c) Length of swing
d) Height of swing
Explanation: In the case of Wallace surface dynamometer, if the surface to be tested is smooth, there will be less friction and pendulum swings for a longer time period. So, time of swing of pendulum is a direct measure of surface finish.
12. Which of the following is a destructive method in measuring surface finish?
a) Gloss measurement
b) Taper sectioning
c) Diffraction technique
d) Micro interferometer
Explanation: In taper sectioning method, a section is cut through the surface to be inspected at a shallow angle, thus magnifying height variations by a factor of cot theta, and the section is studied by optical microscope. It is an accurate but destructive method.
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