Question

The following Figure shows the reading obtained while measuring the diameter of a wire using a screw gauge. The screw advances by 1 division on the main scale when the circular head is rotated once. Calculate:
(i) the pitch of the screw gauge,
(ii) Least count of the screw gauge, and

(iii) The diameter of the wire.

Answer 1

Since the screw advances by 1 division on the main scale when the circular head is rotated once
So, the pitch of the screw = 1mm
The number of divisions= 50
Least count = pitch/number of divisions

= 1/50 = 0.02 mm
Now for the reading shown in the figure,
The main scale reading = 4 mm

From the figure, it is clear that base Line coincides with the 47^th division of the circular scale.
So, circular scale reading = 47 x 0.02 mm = 0.94 cm

Hence, reading shown in the figure = 4+0.94 = 4.94 cm