If the screw on a screw-gauge is given six rotations,
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:

1. (1) $0.001 \mathrm{~cm}$

2. (2) $0.02 \mathrm{~mm}$

3. (3) $0.01 \mathrm{~cm}$

4. (4) $0.001 \mathrm{~mm}$

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. $=\frac{\text { Pitch }}{\operatorname{CSD}}=\frac{0.5 \mathrm{~mm}}{50}$

$=\frac{1}{100} \mathrm{~mm}=0.01 \mathrm{~mm}=0.001 \mathrm{~cm}$

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