This set of Surveying Multiple Choice Questions & Answers (MCQs) focuses on “Field Astronomy – Sextant”.
1. Which of the following can be used to sight two different objects simultaneously?
a) Compass
b) Sextant
c) Theodolite
d) Abney level
View Answer
Explanation: A sextant involves in sighting two different objects simultaneously, which can be able to determine the angle between them. Horizontal as well as vertical angles can be measured with the help of sextant.
2. Sextant can be used to measure vertical angles.
a) True
b) False
View Answer
Explanation: Sextant involves in the measurement of both vertical and horizontal angles. It consists of a movable arm by which the readings can be taken. It is based on the successive reflection of light ray.
3. Which of the following is not a classification of sextant?
a) Box sextant
b) Nautical sextant
c) Vibrating sextant
d) Sounding sextant
View Answer
Explanation: Sextant is used in the measurement of vertical and horizontal angles, which has been classified based on various purposes. Those include box sextant, nautical sextant and sounding sextant.
4. Which of the following can justify the principle of sextant?
a) β = α/2
b) α = β*2
c) α = β+2
d) α = β-2
View Answer
Explanation: Sextant is based on the principle that when a ray of light is reflected successively from two mirrors, the angle between the first and last directions of ray is twice the angle between the planes of two mirrors which can be mathematically represented as α = β/2.
5. Which of the following doesn’t serve as an optical requirement in case of sextant?
a) Optical axis must be parallel
b) Mirrors if placed parallel should be zero
c) Mirrors must be perpendicular
d) Optical axis must be perpendicular
View Answer
Explanation: The optical requirement of sextant include possession of two mirrors which should be perpendicular if parallel mirrors are placed reading should be zero and the optical axis must be parallel to plane of graduated arc.
6. Which classification of the sextant is used for navigation purposes?
a) Box sextant
b) Nautical sextant
c) Vibrating sextant
d) Sounding sextant
View Answer
Explanation: The nautical sextant is used in case of navigational purposes. This can be also used in case of astronomical purpose, it so used because it is a very large instrument graduated with a silver arc about 15 to 20cm.
7. Which of the following instruments can be used for locating inaccessible points?
a) Sounding sextant
b) Vibrating sextant
c) Box sextant
d) Nautical sextant
View Answer
Explanation: A box sextant, which is very small and easily transportable, it is used in the location of inaccessible points. It is also used for measuring horizontal and vertical angles and measuring chain angles.
8. Among the following, which doesn’t come under permanent adjustment of sextant?
a) Index glass perpendicular with graduated arc
b) Horizon glass perpendicular with graduated arc
c) Line of sight parallel to plane of graduated arc
d) Line of sight perpendicular to plane of graduated arc
View Answer
Explanation: The permanent adjustments include making index glass perpendicular with graduated arc, horizon glass perpendicular with graduated arc, and line of sight parallel to plane of the graduated arc etc. these are required for every instrument for having a better output.
9. Which of the following need not to be changed in case of box sextant?
a) Line of sight
b) Index glass
c) Index error
d) Lens
View Answer
Explanation: At the time of manufacturing, the index glass is permanently fixed at right angles to the plane of the instrument. It also doesn’t need a parallel line of sight, as it is already fixed.
10. If the index error is not large, error must be corrected.
a) False
b) True
View Answer
Explanation: If the index error is not large, it is recommended not to correct the error. But the corrections need to be applied to the observed readings. We must have a clear idea of the index error from time to time.
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