Quick questions on Measurement of length and time explained: O-Level Physics

The precision of an instrument is the smallest change it can read. Match the instrument to the size and required precision of the object.

The main scale on the sleeve reads to $0.5\ \text{mm}$, and the thimble is divided into $50$ divisions each worth $0.01\ \text{mm}$. The reading is the sleeve value plus the thimble divisions times $0.01\ \text{mm}$.

A zero error happens when an instrument does not read zero when it should (jaws fully closed, nothing between them). If it reads $+0.02\ \text{mm}$ when closed, every reading is $0.02\ \text{mm}$ too high, so subtract that. A negative zero error is added.

Parallax error is reading a scale from the wrong angle, so the mark appears to line up with the wrong value. Avoid it by looking straight down (eye directly above the mark) so the line of sight is perpendicular to the scale.

A stopwatch has a reading uncertainty, and your reaction time adds error each time you start and stop it. To time something fast and repeating, such as a pendulum, time many oscillations and divide, and repeat the whole timing for an average.

State which instrument you would use to measure the diameter of a thin copper wire, and give its precision. [2 marks]

A micrometer reads $0.03\ \text{mm}$ when the jaws are fully closed. A measurement gives $4.55\ \text{mm}$. State the true value.

Explain why a student times $25$ swings of a pendulum rather than one. [2 marks]