MCQ practice · SSC Physics Board questions · Chapter 1: Physical Quantities and Their Measurements
Which instrument is used to measure the diameter of a thin solid wire?
Think it through first, then pick an option.
- a metre scale
- b screw gauge
- c slide calipers
- d vernier scale
Answer and explanation
Correct answer: b screw gauge
The screw gauge has a least count of 0.01 mm, the finest of the three, so a thin wire's diameter is measured with it.
Why the other options are wrong
- a metre scale: A metre scale reads only up to a millimetre; a thin wire's diameter needs fractions of a millimetre, so it is not fine enough.
- c slide calipers: In the book's example the calipers' VC is 0.1 mm, ten times coarser than the screw gauge's 0.01 mm; a thin wire calls for the screw gauge.
- d vernier scale: The vernier scale is not a separate instrument but a part of the slide calipers; for a wire's diameter the finer instrument is the screw gauge.
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