# Engineering Metrology Questions and Answers – Surface Contour Test

This set of Engineering Metrology Multiple Choice Questions & Answers (MCQs) focuses on “Surface Contour Test”.

1. Which is the wavelength of a spectrum which is used in surface contour test?
a) 0.0005 mm
b) 0.005 mm
c) 0.05 mm
d) 0.5 mm

Explanation: Surface contour test is used to study surface contours and an optical flat is kept at some inclination over the surface. Generally, daylight is used for this test. Wavelength of the spectrum of daylight is 0.0005 mm.

2. How much change is the elevation of surface corresponds to the single fringe interval in surface contour test?
a) 0.0005 mm
b) 0.0025 mm
c) 0.025 mm
d) 0.05 mm

Explanation: In surface contour test, the change in elevation of surface corresponds to each fringe interval shows clearly the precision of this method. Value of this change in elevation is 0.0025 millimeter.

3. If any surface has a scratch on it and surface is tested by surface contour test then, what is the depth of scratch? (D= distance between fringes, d= distance due to scratch)
a) (d/D)*(λ)
b) (d/D)*(λ/2)
c) (d/D)*(λ/4)
d) (d/D)*(3λ/2)

Explanation: Surface contour method is used for many purposes. It is possible to determine depth of the scratch, high and low spots or hills and valleys, and surface worn at the edges. These all can be determined by this method.

4. What is the method to find low and high spots?
a) Pressure by weight test
b) Volume test
c) Pressure test
d) Density test

Explanation: Two low or high spots can be checked by pressure test. If pressure is applied at a point and fringes move closure than the surface is valley. By applying pressure if fringes move apart then the surface is hill.

5. Which of the following option is true for given statements about surface contour test?
Statement 1: In a monochromatic light, bands are lighter near the point of contact.
Statement 2: To study surface contour it is important to know the point of contact with optical flat.
a) T, T
b) F, F
c) F, T
d) T, F

Explanation: For study, it is important to know where surface and optical flat are in contact. Point of contact is usually where a pressure is applied and air film is squeezed at this place.
Bands are sharper near the point of contact in monochromatic light.

6. Curvature of bands is more. What does this statement indicate when surface is tested under surface contour test?
a) More convexity
b) More concavity
c) Flat surface
d) More scratches

Explanation: The magnitude of concavity and convexity can be had by bands curvature. If the band curvature is more it shows more convexity and opposite to this indicates concavity. So we can have an idea of concavity or convexity by this.

7. Which of the following is not true for optical flats used in surface contour test?
a) Colourless
b) Always wrung on the work piece
c) Work piece and optical flat should be free from dust, dust and fingerprints
d) Optical flat should always be lifted from work piece

Explanation: Optical flats should never be wrung on surface to be measured because it scratches too readily. Optical flats should be rested on work piece carefully. It should be clean and free from dust.

8. What is the nature of the surface if curve bands around the line of contact when the surface is tested under surface contour test?
a) Convex surface
b) Concave surface
c) Flat surface
d) May be convex or concave

Explanation: If band curves around the line of contact or point then the given surface is convex but if the band curves opposite to the line of contact or point then the surface is a concave surface.

9. Given figure is a surface to be tested by surface contour test. How much lower or higher is B than Z in this given figure?

a) λ/4
b) λ/2
c) 3λ/2
d) 3λ/4

Explanation: In the given figure, BYB is the contour. Y and Z are at the centre of two contours. The edge B is either higher or lower than Z by λ/2. The air gap will increase if we move away from X-X. BYB represents points at equal height, it means that B is higher than Z.

10. How much height intervals relative to optical flat is represented by a spacing of fringes?
a) λ/3
b) λ
c) λ/2
d) λ/6

Explanation: Contour of every fringe lies on points of equal height relative to the surface of optical flat. So, the fringe pattern viewed through optical flat will represent the contour map of the surface under test and spacing of fringes will represent height intervals relative to the optical flat of λ/2.

Sanfoundry Global Education & Learning Series – Engineering Metrology.

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