Question

If the screw on a screw-gauge is given six rotations, it moves by $3\text{mm}$ on the main scale. If there are $50$ divisions on the circular scale, the least count of the screw gauge is:

• A. $0.001\text{cm}$
• B. $0.02\text{cm}$
• C. $0.01\text{cm}$
• D. $0.002\text{cm}$

Answer 1

The correct option is A $0.001\text{cm}$

$\text{Pitch}=\frac{\text{linear distance travelled by the screw}}{\text{number of rotations}}$

$\therefore \text{Pitch}=\frac{3}{6}=0.5\text{mm}$

$\therefore \text{Least count}=\frac{\text{Pitch}}{CSD}=\frac{0.5}{50}$

$=0.01\text{mm}=0.001\text{cm}$

Hence, $\left(A\right)$ is the correct answer.