# Engineering Metrology Questions and Answers – Flatness Testing

This set of Engineering Metrology Multiple Choice Questions & Answers (MCQs) focuses on “Flatness Testing”.

1. For checking the flatness, which of the following is used to mark the surface?
a) Scriber
b) Prussian blue
c) Alcohol
d) Ruler

Explanation: Prussian Blue is used to mark the surface. When rubbed against another flat surface, the distribution of color on the other surface gives a rough idea of flatness of the surface.

2. Determination of flatness using Prussian blue is used for which kind of surfaces?
a) Small surfaces
b) Large surfaces
c) Both large and small surfaces
d) For surfaces with fine smoothness

Explanation: This method is suitable for small surfaces rather than large surface. This method is assumptious and may give more errors in determination of flatness in large surfaces.

3. As per IS: 2063-1962, which surface is considered as a flat surface?
a) When variation of perpendicular distance from geometrical reference plane remains above a given point
b) When variation of diagonal distance from geometrical reference plane remains below a given point
c) When variation of perpendicular distance from geometrical reference plane remains below a given point
d) When variation of sides distance from geometrical reference plane remains above a given point

Explanation: As per IS: 2063-1962, a surface is considered flat when the variation of perpendicular distance from geometrical reference plane parallel to the general trajectory same as the surface to be tested remains below a given point. The reference plane can be represented by means of surface plane or family of straight lines.

4. When the flatness is measured with the use of optical flats, at what distance bands should be viewed?
a) Distance 10 times the diameter of optical flats
b) Distance 5 times the diameter of optical flats
c) Distance 8 times the diameter of optical flats
d) Distance 2 times the diameter of optical flats

Explanation: The bands are viewed from a distance at least 10 times the optical flat diameter and with the line of vision are perpendicular to the flat. If the bands observed are parallel, straight and evenly spaced, the surface is flat otherwise not.

5. Which of the following method is used for the determination of flatness when the surface is irregular?
a) Half grid method
b) Grid method
c) Contact method
d) Non contact method

Explanation: When the surface is irregular, contact method of testing for flatness is used. In the contact method there is a most intimate possible contact between flat and work piece and there will be attempt to maintain a wedge.

6. Which of the following option is true for given statements for flatness testing?
Statement 1: Straight edges can be used to check flatness.
Statement 2: Single ended straight edge can be used to determine flatness of the surface.
a) T, T
b) F, F
c) T, F
d) F, T

Explanation: Straight edges can be used to test flatness and straightness of the surfaces. Single-edged straight edge can be used to determine flatness by applying it at different places in different directions on the tested surface.

7. Which of the following option is not true for flatness testing?
a) Geometrical plane can be represented by a family of straight lines
b) Flatness can be tested by grid and half grid method
c) Three and four edge type straight edge cannot be used for this purpose
d) Geometrical plane can be represented by a surface plane

Explanation: Three and four edges straight edges can be used to test flatness by applying prussian blue on the working edges and then drawing the straight edge across the surface.

8. What are the requirements for the measurement of flatness using light?
a) Monochromatic light and a pair of optical flats
b) Dichromatic light and sets of optical flats
c) White light and a pair of optical flats
d) Monochromatic light and sets of optical flats

Explanation: Monochromatic light and sets of optical flats are required for measurement of flatness using light. Monochromatic light is used to get none overlapping, clear interference pattern.

9. What is flatness error?
a) Maximum separation of a pair of parallel planes which will contain all points on the surface
b) Minimum separation of a pair of parallel planes which will contain all points on the surface
c) Minimum separation of a pair of perpendicular planes which will contain all points on the surface
d) Maximum separation of a pair of perpendicular planes which will contain all points on the surface

Explanation: Flatness error can be defined as the minimum separation of a pair of parallel planes which will contain all points on the surface. Deviations of large surfaces from true plane are determined by using autocollimator and spirit level.

10. Which of the following is true for testing flatness with optical flats?
a) Too large angle of work with flat is desirable
b) Number of bands appears is an indication of flatness
c) Bands are viewed as perpendicularly as possible
d) Quartz flats are very sensitive to temperature changes

Explanation: Due to very great angle between work and flats, bands will be close together and are nearly invisible. Number of bands appear is not an indication of the surface flatness but relates only to the wedge steepness.

11. What is the range of the diameter of optical flats used in testing the flatness?
a) 25mm to 300mm
b) 1mm to 100mm
c) 50mm to 500mm
d) 1mm to 10mm

Explanation: Size of optical flats used varies from 25mm to 300mm diameter. The range is selected to get a proper interference pattern using light.

Sanfoundry Global Education & Learning Series – Engineering Metrology.

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