In a screw gauge, the zero of the circular scale lies 3 divisions above the horizontal pitch line when their metallic studs are brought in contact. Using this instrument thickness of a sheet is measured. If pitch scale reading is 1 mm and the circular scale reading is 51 then the correct thickness of the sheet i $s ______$ mm.
[Assume least count is 0.01 mm]

Question

In a screw gauge, the zero of the circular scale lies 3 divisions above the horizontal pitch line when their metallic studs are brought in contact. Using this instrument thickness of a sheet is measured. If pitch scale reading is 1 mm and the circular scale reading is 51 then the correct thickness of the sheet i $s ______$ mm.

[Assume least count is 0.01 mm]

G1 Physics · Accepted Answer

When the zero of the circular scale lies above the reference line, the zero error is negative. Therefore, zero error = -3 × least count = -3×0.01 = -0.03 mm. Observed reading: reading = pitch-scale reading + circular-scale reading × least count = 1.00 + 51×0.01 = 1.51 mm. Correct reading is correct reading = observed reading - zero error = 1.51 - (-0.03) = 1.54 mm. Correct option: C.