Name the instrument which can measure accurately the following —

1. the diameter of a needle,
2. the thickness of a paper,
3. the internal diameter of the neck of a water bottle,
4. the diameter of a pencil.

Which of the following measures a small length to a high accuracy — metre rule, vernier callipers, screw gauge?

Explain the meaning of the term ‘least count of an instrument’ by taking a suitable example.

A boy makes a ruler with graduation in cm on it (i.e., 100 divisions in 1m). To what accuracy this ruler can measure ? How can this accuracy be increased ?