GATE CE 2015 Set 2 — Question 65
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Geomatics Engineering → Levelling → Reciprocal Levelling
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Question
Two Pegs A and B were fixed on opposite banks of a wide river. The level was set up at A and the staff readings on Pegs A and B were observed as and , respectively. Thereafter the instrument was shifted and set up at B. The staff readings on Pegs B and A were observed as and , respectively. If the R.L. of Peg A is , the R.L. (in m) of Peg B is __________.
Correct answer
100 to 100
Solution
This is a problem of reciprocal leveling to eliminate errors due to curvature, refraction, and imperfect adjustment of the line of collimation.Let be the readings from station A on pegs A and B respectively:
Let be the readings from station B on pegs A and B respectively:
(reading on A from B)
(reading on B from B)The true difference in elevation () between A and B is given by:
Since the readings on B are consistently higher than on A, B is at a lower elevation than A.
.
Let be the readings from station B on pegs A and B respectively:
(reading on A from B)
(reading on B from B)The true difference in elevation () between A and B is given by:
Since the readings on B are consistently higher than on A, B is at a lower elevation than A.
.
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