68 Questions
What is the main purpose of compass surveys?
To provide rapid filling of details in larger surveys
When is chain survey preferred over compass survey?
For small areas where high accuracy is needed
What is one major drawback of using a compass for determining the bearing of a line?
The compass needle aligns inconsistently with the magnetic field
What is the main use of a prismatic compass?
For measuring magnetic bearings
Why should care be taken when using a compass survey?
To prevent magnetic disturbances from affecting results
Which type of survey is mainly used for rapid filling of details in larger surveys?
Compass survey
What is the main difference between the Prismatic Compass and the Surveyor's Compass?
The Surveyor's Compass is generally used on a stand or tripod.
What is the purpose of the 45º reflecting prism in the Prismatic Compass?
To adjust the focus of the image of the graduations.
What is the function of the lifting pin and lifting lever in the Prismatic Compass?
Lifting the magnetic needle out of the pivot to prevent damage.
Which part serves as the heart of the Prismatic Compass?
Magnetic needle.
Why do the graduations on the Prismatic Compass remain stationary with the needle?
To enable reading off the graduated arc directly.
What is the purpose of the mirror located in front of the forward vane in the Prismatic Compass?
To provide solar observations.
Why is the graduated circle or ring in the Prismatic Compass marked from 0º to 360º?
To measure all possible bearings of lines.
What does the object vane in a Prismatic Compass carry?
Horse hair or black thin wire to sight object in line with eye sight.
What is a non-magnetic metal case with a glass top in a Prismatic Compass known as?
Cylindrical metal box.
What part of a Prismatic Compass carries a fine slit provided with an eye hole at bottom?
Eye vane.
What is the main purpose of a surveyor's compass?
To determine the magnetic bearing of a line
How is the bearing measured in a surveyor's compass?
Clockwise starting from North
What is the difference between Fore Bearing (FB) and Back Bearing (BB)?
FB is taken in the direction of survey, BB is taken in the opposite direction
If a Fore Bearing is 1200, what would be the corresponding Back Bearing?
1800
How is a traverse plotted after traversing with the compass?
By considering the general shape of the area
What system measures the bearing in quadrants starting from North?
Quadrantal Bearing System (Q.B)
What does Reduced Bearing (R.B) refer to?
Bearing converted from Whole Circle Bearing to Quadrantal bearing
In what direction are survey lines measured in Quadrantal Bearing System?
Both clockwise and anti-clockwise
'The bearing of a line measured with respect to magnetic meridian in clockwise direction.' Which system does this statement describe?
'Whole Circle Bearing System (W.C.B.)'
'In this system, the bearing of survey lines are measured wrt to north line.' Which system is being referred here?
'Quadrantal Bearing System (Q.B.)'
What is the purpose of using sun glasses in the prismatic compass?
To bisect luminous objects
How is the centering of the prismatic compass checked?
By dropping a pebble from the underside
What is the purpose of levelling the compass in a prismatic compass operation?
To ensure that the compass can rotate freely
What does the term 'whole circle bearing' refer to in a prismatic compass operation?
A bearing that covers 360 degrees clockwise
What is the reason behind variations in magnetic declination mentioned in the text?
Related to movements of the magnetic poles
What is the secular variation related to magnetic declination?
It is a slow continuous swing with a cycle of about 400 to 500 years
How is the magnetic bearing of a survey line defined?
The angle between magnetic meridian at starting and ending points
What defines the direction of a magnetic meridian at any place?
The direction obtained by observing a freely supported magnetized needle
'Angle of Declination' is defined as:
The angle between magnetic meridian and true meridian
How does Diurnal Variation differ from Secular Variation in terms of time frame?
Diurnal Variation is a minor variation during certain periods, whereas Secular Variation has large continuous swings over centuries.
What is local attraction in compass survey?
Influence that prevents magnetic needle from pointing to the magnetic north pole
How is local attraction detected in a compass survey?
By observing both bearings of a line and noting the difference
What is the first method used to eliminate local attraction?
Checking the difference of F.B. & B.B. of each line of traverse
In a closed traverse, what is a check available for angular error?
Sum of interior angles should equal (2n-4) x right angle
What does the transit rule apply to in surveying?
Angular measurements
What is levelling in surveying?
Establishing height above or below a datum line
What is a level surface in levelling?
A surface parallel to the mean spheroid of the earth
How is horizontal surface defined in levelling?
A surface parallel to level surfaces at a specific point
What is the role of inspection compasses in surveying?
Detecting and eliminating local attraction errors
What is the point or surface with respect to which levels of other points or planes are calculated called?
Datum
What is the average height of the sea of all stages of tides known as?
Mean sea level
What is a relatively permanent point of reference with a known elevation w.r.t. a datum called?
Bench mark
Which instrument provides a horizontal line of sight and magnifies readings far away from it?
Dumpy level
What is the main advantage of a dumpy level over a wye level?
Solid construction
What is a levelling staff used for?
Taking horizontal sight readings
What imaginary line is horizontal when the bubble in the telescope is centered?
'Axis of level tube'
What is the main purpose of differential leveling in surveying?
To determine difference in elevations of two points
What is another term for 'Fly Leveling' as mentioned in the text?
Profile Leveling
In surveying, what is the purpose of taking back sight readings at turning points?
To adjust the height of the instrument
What is the method used to calculate Reduced Levels in differential leveling?
Height of Instrument method
What does the arithmetic check ΣB.S - ΣF.S = ΣRISE - ΣFALL represent in surveying?
Verification of closure error in leveling
Why is setting up turning points necessary in differential leveling?
To enable taking back sight and fore sight readings
What is the term for the operation of bringing the clear image of an object into the plane of cross hairs in a telescope?
Focusing
What is the error that occurs when the bubble is not in the center of the run in a bubble tube?
Error due to Sensitiveness
In levelling, what is the term for the last reading taken from an instrument just before shifting it?
Fore sight
What is the term for a point on which both fore sight and back sight are taken?
Change point
Which type of levelling involves determining the difference in levels of two nearby points?
Simple levelling
What is the term for carrying out levelling with respect to a temporary bench mark?
Fly levelling
Which type of levelling involves finding reduced levels of various points at regular intervals along a line or set of lines?
Profile levelling
What kind of telescope is externally focused by moving either the objective or eye piece?
External focusing telescope
What is eliminated by making the lengths of two sides equal in a bubble tube?
Error due to Curvature
What is the term for the type of levelling used when it's not possible to balance fore sight and back sight due to various errors?
Reciprocal levelling
Learn about the essential process of focusing in a telescope, involving adjusting the eye piece and objective to form a clear image at the fixed plane of cross hairs. Explore the steps involved in complete focusing and different types of telescopes.
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