Measuring Instruments & Errors — A/L Physics

What must I remember about Measuring Instruments & Errors?

• Least Count (LC): The smallest value that can be directly measured by an instrument. Vernier Caliper LC = 1 MSD - 1 VSD (typically 0.1 mm); Micrometer Screw Gauge LC = Pitch / Number of circular divisions (typically 0.01 mm); Spherometer LC = Pitch / Head scale divisions (typically 0.01 mm).
• Zero Error and Zero Correction: Zero error is positive if the zero mark is ahead/to the right of reference index; Zero correction is always the NEGATIVE of zero error (True Reading = Observed Reading - Zero Error).
• Systematic Errors vs Random Errors: Systematic errors consistently shift readings in one direction (instrument calibration, zero error, end error); Random errors fluctuate unpredictably (parallax, temperature drift, human reaction).
• Fractional and Percentage Uncertainties: If y = a + b, absolute uncertainty Δy = Δa + Δb; If y = (a^m * bⁿ) / c^p, fractional uncertainty Δy/y = m(Δa/a) + n(Δb/b) + p(Δc/c).

Test yourself (1 minute)

1. Minimizing percentage error

   To minimize percentage error in experiments, choose measuring instruments such that the measured dimension is large compared to the least count (e.g., measuring thickness of 100 sheets instead of 1).

2. Micrometer ratchet mechanism

   Prevents overtightening and deformation of specimen by slipping when uniform pressure is reached.

3. Backlash Error

   Caused by wear in screw threads; eliminated by always rotating the thimble in one continuous direction during measurement.

Practise Measuring Instruments & Errors questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 1: Measurement

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Where does Measuring Instruments & Errors fit in the syllabus?

Unit 1.4 · Year 1 · Term 1