Question

Name the instrument which has the least count of $0.1mm$.
A) Vernier calipers B) Screw gauge C) Meter scale D) All of the above

Answer 1

Hint: The least count of a measuring instrument is the least amount of measurement that we can take using that device. Vernier Calipers, screw gauge and meter scale, all are instruments that are used to measure length.

Complete step-by-step answer:
The least count of a length measuring device is essentially the length measured by the smallest division on the scale.
The most commonly used and calibrated vernier calipers have a least count of $0.1mm$. The ${{10}^{th}}$ division of the main scale coincides with the ${{9}^{th}}$ division of the main scale. Each main scale division is of length $1mm$ while the least count is $1-\dfrac{9}{10}=\dfrac{10-9}{10}=\dfrac{1}{10}mm=0.1mm$ (Since the least count of a vernier caliper is given by $1MSD-1VSD$), where $MSD$ stands for main scale division, while $VSD$ stands for vernier scale division.
Hence, the correct option is A) Vernier calipers.
Additional information:
The least count of the most common form of the screw gauge (also known as a micrometer) is $0.01mm$. The least count of a metre scale is $1mm$. It has $100$ main divisions each of $1cm$ length. Each main division is divided into ten smaller divisions measuring $1mm$ each. Hence, the least count of the metre scale is $1mm$.
Note: Students must properly know the least counts and the procedures to calculate the least counts of various length measuring instruments since this knowledge is very important not only from an examination point of view, but also while performing experiments in the laboratory. The procedure for finding the least count for the vernier calipers is especially important since the same principle is used in other instruments also, such as the angular vernier scale which measures angles instead of length.