A screw gauge has 100 divisions on its circular scale and a pitch of 1 mm. When the jaws are closed, the 5th division of the circular scale is observed to be coinciding with the main line, and the zero of the circular scale is below the main line. When a wire is measured, the main scale reading is 3 mm and the 35th division of the circular scale coincides. What is the correct diameter of the wire?

7 views 1 helpful Updated Jul 26, 2026
Appears in NEET UG
Solution ✔ Verified
  • A3.30 mm
  • B3.35 mm
  • C3.40 mm
  • D3.45 mm
Explanation

Least Count (LC) = Pitch / Number of divisions = 1 mm / 100 = 0.01 mm. The zero of the circular scale is below the main line and the 5th division coincides, indicating a positive zero error of + (5 * LC) = + (5 * 0.01 mm) = +0.05 mm. Observed Reading = Main Scale Reading + (Circular Scale Reading * LC) = 3 mm + (35 * 0.01 mm) = 3 mm + 0.35 mm = 3.35 mm. Corrected Reading = Observed Reading - Zero Error = 3.35 mm - (+0.05 mm) = 3.30 mm.

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