Paper 2 · November 2017 · Measurement and Units
A micrometer screw gauge is used to measure the diameter of a small workpiece. Which of the following is a correct precaution to take when using this instrument?
AUse the ratchet to avoid over-tightening on the workpiece.
BTighten the thimble as hard as possible to get a firm grip.
CImmerse the jaws in water after each measurement to keep them clean.
DLeave the jaws fully closed and store the instrument in direct sunlight.
Explanation
The ratchet lets the user apply a consistent, gentle force and stops over-tightening, which would damage the instrument or crush the workpiece. Over-tightening, wetting the jaws, and sunlight storage are all poor practice.
Derived from ZIMSEC Physics 5055/2 Paper 2 Theory, November 2017, Q1