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UPSC Civil Service Exam Questions - Engineering

Q1:

In an external focusing tachometer, the fixed interval between static hairs is 5 mm, the focal length of the objective is 25 cm, and the distance of the vertical axis of the instrument from the optical centre of the objective is 15 cm. Which one of the following is the set of constant of the tachometer ?

A 30, 0.15

B 30, 0.40

C 50, 0.25

D 50, 0.40

ANS:D - 50, 0.40

K and C are the tacheometric constants.

K= f/I = (25/0.5) = 50,
C= f+d = (0.25 + 0.15) = 0.4.