In a subtense bar method, a micrometer screw had to be moved for
| In a subtense bar method, a micrometer screw had to be moved for staff intercept of 2.0 m, with the staff held vertical at a distance of 120 m from the instrument. The vertical angle was 5° and tachometric constants are 1000 and 0.5. The total no of turns made by micrometer screw –
A. 16.61
B. 18.61
C. 19.88
D. 14.61
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Right Answer is: A
SOLUTION
In subtense bar method.
\(D = \;\frac{{KS}}{m}{\cos ^2}\theta + C.\cos \theta \) (For inclined line of sight)
Here, D = 120 m, K = 1000, S = 2 m, C = 0.5, θ = 5°, m = no of turns by micrometer screw
\(\therefore 120 = \frac{{1000 \times 2}}{m}{\cos ^2}5 + 0.5\cos 5\)
m = 16.61