Least Count And Instruments

Question

A workshop technician uses a screw gauge whose pitch is 1 mm and whose circular scale carries 100 equal divisions to measure a thin metal sheet. What is the least count of this instrument?

RankGuru · Accepted Answer

As described in NCERT Class 11, Chapter 2 (Units and Measurements), the least count of a screw gauge is the smallest length it can reliably measure and equals the pitch divided by the number of divisions on the circular scale. The pitch is the linear distance moved by the screw in one full rotation, here 1 mm, and the circular scale has 100 divisions. Therefore the least count is 1 mm / 100 = 0.01 mm. The option 0.1 mm is wrong because it divides by only 10 instead of 100. The option 0.001 mm is wrong as it divides by 1000, overstating the instrument's resolution tenfold. The option 1 mm is wrong since that is the pitch itself, not the least count. A final plausibility check confirms that a least count of 0.01 mm is typical for a standard micrometer screw gauge, making it suitable for measuring a thin metal sheet.

Least Count And Instruments

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