Question

Two full turns of the circular scale of a screw gauge cover a distance of 1 mm 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 -0.03 mm while measuring the diameter of a thin wire, a student notes the main scale reading of 3 mm and the number of circular scale divisions in line with the main scale as 35. The diameter of the wire is:

• A. 3.32 mm
• B. 3.73 mm
• C. 3.67 mm
• D. 3.38 mm

Answer 1

The correct option is D 3.38 mm

Pitch,
$p=\frac{1mm}{2}$
$p=0.5mm$

Least count,
$LC=\frac{p}{50}$
$LC=\frac{0.5mm}{50}$
$LC=0.01mm$

Using the formula for the measurement using screw gauge, diameter is:
$d=MSR+(CSR\times LC)+ZE$
$d=3+35\times 0.01+0.03$
$d=3.38mm$