Question:
If the screw on a screw-gauge is given six rotations, it moves by $3 \mathrm{~mm}$ on the main scale. If there are 50 divisions on the circular scale the least count of the screw gauge is:
Correct Option: 4
Solution:
(4) When screw on a screw-gauge is given six rotations, it moves by $3 \mathrm{~mm}$ on the main scale
$\therefore \quad$ Pitch $=\frac{3}{6}=0.5 \mathrm{~mm}$
$\therefore \quad$ Least count L.C. $=\frac{\text { Pitch }}{\operatorname{CSD}}=\frac{0.5 \mathrm{~mm}}{50}$
$=\frac{1}{100} \mathrm{~mm}=0.01 \mathrm{~mm}=0.001 \mathrm{~cm}$