Question

The thickness of the wall of a chemical laboratory test tube is $0.2566cm$. Which of the following could have been the measuring instrument used to find the thickness value?

• A. Ordinary screw gauge
• B. Micrometre screw gauge
• C. Ordinary vernier callipers
• D. Metre ruler

Answer 1

The correct option is B Micrometre screw gauge

Given:
Thickness of a test tube wall = $0.2566cm$
This measurement is precise upto 4 decimal places.
So, to identify the measuring instrument, we need to simply know the least counts of the given instruments.
Amongst the given options,

• The metre ruler has a least count of $0.1cm$.
• An ordinary vernier calliper has a least count of $0.01cm$.
• An ordinary screw gauge has a least count of $0.001cm$.

These cannot be the instrument used, because their least counts are accurate only upto 1, 2 and 3 decimal places respectively.
The least count of a micrometre screw gauge = $1\mu m$ or $0.001mm$ or $0.0001cm$, which has an accuracy upto 4 decimal places. So, it could have been the instrument used.