# Engineering Metrology Questions and Answers – Test for Straightness by using Spirit Level and Autocollimator

This set of Engineering Metrology Interview Questions and Answers for Experienced people focuses on “Test for Straightness by using Spirit Level and Autocollimator”.

1. How the straightness of any surface can be determined with the help of spirit level?
a) By finding relative angular positions at extreme sections of the surface
b) By finding relative linear distance at middle of the surface
c) By finding relative angular positions at adjacent section
d) By finding relative angular positions at any point

Explanation: In case of the spirit level, the angular variations are measured by the sensitive level on it which gives the difference of height between two points by knowing the spirit level’s least count.

2. At what distance instrument is placed when straightness is determined with the help of autocollimator?
a) 0.5 to 0.75 mm
b) 0.5 to 0.75 cm
c) 0.5 to 0.75 m
d) 0.5 to 0.75 µm

Explanation: In determining the straightness with the help of autocollimator instrument is placed at a distance of 0.5-0.75 m on any rigid support and it is completely independent of the surface to be tested.

3. For testing straightness with the help of spirit level, what is the length of each surface section?
a) Equal to spirit level base length
b) Greater than spirit level base length
c) Less than spirit level base length
d) Doesn’t depend upon spirit base length

Explanation: For determining straightness, a straight line is drawn on the surface. It is divided into sections, the length of individual section is equal to the length of the base of spirit level or the base of a reflector in case of autocollimator.

4. For which surfaces, spirit level is used for testing straightness?
a) Both horizontal and vertical surfaces
b) Vertical surfaces
c) In any plane
d) Horizontal surfaces

Explanation: In testing straightness, spirit level is used only for the horizontal surfaces while autocollimator can be used in any plane. In the case of spirit level, angular variations are measured by placing level on it.

5. Which of the following option is true for autocollimators?
Statement 1: Electronic autocollimator has more resolution than visual autocollimator.
Statement 2: Observations are taken using precision level.
a) F, F
b) F, T
c) T, T
d) T, F

Explanation: Electronic autocollimator has 100 times more resolution than visual autocollimator. Visual autocollimator can measure small angles like 0.5 arc minute. Electronic autocollimator can be used for stable platform applications.

6. 1 sec of arc will correspond to how much rise or fall in surface, when surface straightness is tested by autocollimator? (λ is the distance between centres of feet)
a) 0.000006λ
b) 0.00006λ
c) 0.00006λ
d) 0.0006λ

Explanation: In this method, reading of tilt of the reflector is taken in seconds from the eyepiece. 1 second of arc is 0.000006 mm/mm. It also depends upon the distance between feel centres in millimeter.

7. Which of the following is not true for autocollimator?
a) Contact measurement
b) Use for small tilts
c) High sensitivity
d) Used to determine parallelism

Explanation: Autocollimator is used in many applications like in shop floors and metrology labs. Used for precision measurement of parallelism, straightness, flatness, perpendicularity etc. It is a not-contact optical instrument.

8. Which of the following method is used for the mathematical treatment of determination of straightness with the help of autocollimator?
a) Taylor’s principle
b) Least square method
c) Bryan method
d) Average method

Explanation: According to the least square method, ‘sum of the deviations of the points from the best line is zero and the sum of square of deviations from the best line is minimum’. First the best line is determined and then applies to this method.

Sanfoundry Global Education & Learning Series – Engineering Metrology.