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UPSC Civil Service Exam Questions - Engineering

Q1:

In trigonometric levelling, if the horizontal distance between the instrument and the object is 3088 m, the coefficient of refraction is 0.07 and R sin 1" = 30.88 m, then the refraction correction in angular measure would be

A 0.07"

B 0.70"

C 7.0"

D 1'10"

ANS:C - 7.0"

Central angle, a = D/R sin 1" = 3088/30.88 = 100".
Assuming coefficient of refraction, m = 0.07.
Refraction correction = m*a = 0.07*100 = 7" (-).

Curvature correction = a/2 = 100/2 = 50" (+).