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A screw gauge with a pitch of 0.5 mm and a circular scale with 50 divisions is used to measure the thickness of a thin sheet of Aluminium. Before starting the measurement, it is found that when the two jaws of the screw gauge are brought in contact, the 45th division coincides with the main scale line and that the zero of the main scale is barely visible. What is the thickness of the sheet if the main scale reading is 0.5 mm and the 25th division coincides the main scale line ?
- 0.75 mm
- 0.80 mm
- 0.70 mm
- 0.50 mm
Correct answer: 0.80 mm
Solution
To find the thickness of the sheet, we first account for the zero error, which is -0.05 mm (since the 45th division coincides with the main scale line). The main scale reading is 0.5 mm, and the circular scale reading is 25 divisions, which corresponds to 0.5 mm (25/50 of the pitch). Adding these values gives 0.5 mm + 0.5 mm - 0.05 mm = 0.80 mm.
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