# Engineering Metrology Questions and Answers – Terminology as per Indian Standards

This set of Engineering Metrology online test focuses on “Terminology as per Indian Standards”.

1. What do you mean by Geometrical Surface?
a) Surface prescribed by design without any errors of form or surface roughness
b) Surface limiting the body and separating it from surrounding
c) Close representation of real surface
d) Outer surface of the body

Explanation: Geometrical surface is the surface prescribed by design or by process of a manufacturer, neglecting errors of form or surface roughness. Real surface is the surface limiting the body and separating it from surrounding surface.

2. Under which category, does the scratches falls?
a) Lay
b) Effective surface
c) Flaws
d) Geometrical surface

Explanation: Flaws are the type of irregularities which occur at one place or at relatively infrequent or at very widely varying intervals in surface. Scratches, cracks, random blemishes etc. are the type of flaws.

3. Which of the following statement is wrong about sampling length?
a) It is the length of profile necessary for evaluation of irregularities to be taken account
b) It is known as cut off length in regard to measuring instruments
c) It is measured in a direction parallel to general direction of profile
d) It is the length of profile necessary for evaluation of surface roughness parameters

Explanation: Sampling length is the profile length which is necessary for the evaluation of the irregularities. This is also called as the ‘cut-off length’ in regard to the measuring instruments. It is measured in parallel direction to the direction of the profile.

4. What is the general instrument cut off for majority engineering work?
a) 0.08 mm
b) 0.8 mm
c) 0.1 cm
d) 0.5 mm

Explanation: For majority of the engineering work, 0.8 mm is considered to be quite satisfactory for instrument cut-off and for most waviness measurements upper limit of about 25 mm is suitably accepted.

5. What is the upper limit that is commonly accepted for waviness measurement?
a) 10mm
b) 20mm
c) 25mm
d) 15mm

Explanation: There is no theoretical value that could be assigned to maximum spacing for waviness as higher value of waviness tends to merge with other general errors in geometric forms. 25mm is the upper limit commonly accepted as suitable for waviness measurement.

6. What is the correct formula for average wavelength to describe surface roughness? (Where, Ra is the arithmetic mean deviation from the mean line of profile)
a) 2π x Ra / Mean slope
b) 2π x Ra x Mean slope
c) 2π / Ra x Mean slope
d) 2π / Ra / Mean slope

Explanation: Rt is the maximum height of peak to valley within the assessment length. Rt measurement is valuable for providing guidance for planning metal-cutting operations and analysing finish. Average wavelength = 2π x Ra / Mean slope.

7. Which of the following is an effective surface as per Indian standard?
a) A real surface is an effective surface
b) It is the direction of predominant surface pattern
c) Close representation of real surface
d) Real surface which doesn’t represent instrumental means

Explanation: A real surface is the surface which limiting the body and separating it from the surface of surrounding and effective surface is the close representation of real surface which is obtained by instrumental means.

8. Which of the following is true for a mean and center line of profile?
a) When the waveform is repetitive then there is some difference between mean and centre line
b) Mean line of profile is the mean distance between more prominent irregularities
c) Mean line profile is the average value of ordinates from mean line
d) Centre line of profile is the line which is parallel to the direction of profile and area embraced above and below the line is equal

Explanation: Mean line of the profile is the line which have the form of the geometrical profile. Mean line of profile divides the effective profile so that the sum of the squares of distances between effective points and the mean line is a least. When the waveform is repetitive, the centre and mean line are equivalent.

9. What is ten point height of irregularities?
a) Average difference between 10 highest peaks
b) Average difference between 10 deepest valleys
c) Average difference between 5 highest peaks and 5 deepest valleys
d) Average difference between 10 highest peaks and 10 deepest valleys

Explanation: Ten point height of irregularities is represented by Rz and defined as the average difference between the 5 highest peaks and the 5 deepest valleys within the sampling length measured from a line, not crossing the profile and parallel to the mean line.

10. Which of the following is a criterion of a good bearing surface?
a) Positive skew
b) Negative skew
c) Negative peak roughness
d) Positive start up length

Explanation: Skew will show whether porous, sintered and cast iron surfaces will yield a meaningful Ra (arithmetic mean deviation from the mean line of profile) measurement. Negative value of skew is the criterion for a good bearing surface.

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