- A. micrometer screw gauge
- B. pair of dividers
- C. metre rule
- D. pair of vernier calipers ✓
Vernier calipers are precise measuring instruments that are commonly used to measure the inner diameter of objects, such as the inside of a test tube. They consist of a main scale, which is usually graduated in millimeters or inches, and a vernier scale, which is used to make finer measurements. The vernier scale has a smaller graduation than the main scale, allowing for more precise measurements.
To measure the inner diameter of a test tube using vernier calipers, you would first open the jaws of the calipers to a size slightly larger than the interior of the test tube. Then, you would insert the jaws into the test tube and tighten them so that they are held firmly against the inner walls of the tube. Finally, you would read the measurement on the main scale and use the vernier scale to determine the fractional part of the measurement.
In comparison, a micrometer screw gauge is typically used for measuring external dimensions or depths rather than internal diameters. A pair of dividers can be used for marking or scribing circles and arcs but are not suitable for precise linear measurements like inner diameters. A metre rule, while useful for measuring longer distances, lacks the precision required for measuring small dimensions like those found in test tubes.
