Question

Two full terms 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. $3.32mm$
• B. $3.73mm$
• C. $3.67mm$
• D. $3.38mm$

Answer 1

The correct option is D $3.38mm$

Zero Error $=-0.03mm$

The Circular scale covers $1mm$ on the main scale for two rotations.

So the Pitch is $0.5mm$

The circular scale have $50$ div. This means that for $35$ div the reading on main scale is $\frac{0.5}{50}\times 35$

So the Diameter $=$ actual reading - Zero error

$=(3+0.35)+0.03$

$=3.38mm$