Question

Two full turns of the circular scale of a screw gauge cover a distance of 1mm on its main scale. The total number of divisions on the circular scale is 50. Further, it is found that the screw gauge has a zero error of –0.03mm. While measuring the diameter of a thin wire, a student notes the main scale reading of 3mm and the number of circular scale divisions in line with the main scale as 35. The diameter of the wire is

(a) 3.38mm 

(b) 3.32mm

(c) 3.73mm 

(d) 3.67mm.

Answer 1

(a) : Least count of the screw gauge = (0.5mm)/50 = 0.01mm

Main scale reading = 3mm.
Vernier scale reading = 35
Therefore, Observed reading = 3 + 0.35 = 3.35
zero error = –0.03
Therefore, actual diameter of the wire = 3.35 – (–0.03) = 3.38mm.