Question

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

• A. $0.001cm$
• B. $0.01cm$
• C. $0.001mm$
• D. $0.02mm$

Answer 1

The correct option is A $0.001cm$

Given on six rotations, reading of main scale changes by $3mm$.
Also no. of division on circular scale $=50$.
Pitch of screw of a screw gauge,

$\text{Pitch}=\frac{\text{distance moved by screw}}{\text{number of rotations}}$

$=\frac{3mm}{6}=0.5mm$

and least count of screw gauge,
$LC=\frac{\text{Pitch}}{\text{No.of circular scale divisions}}$

$=\frac{0.5mm}{50}=0.01mm=0.001cm$

Final Answer: (a)