Vernier callipers can measure diameter accurate to 0.02 mm. They consist of a main scale showing millimetres and a secondary scale showing the 50 divisions of each millimetre (broken into 0.02 mm sections). The external jaws measure external diameter and the internal jaws, internal diameter.
internal jaws locking screw
metric scale depth measuring blade external jaws FIG. 1.3 Vernier callipers are used to measure internal and external diameter u How to use vernier callipers
1. Place the jaws around the object. 2. Take the reading on the main scale. 3. Find where the secondary scale division lines up closest with the main scale. Add this reading to the first scale to get a total.
For example, in Fig. 1.4 the line representing 24 hundredths of a millimetre on the secondary scale lines up with a division on the main scale. This means the reading is: 19 + 0.24 = 19.24 mm.
Digital callipers (Fig. 1.5) are an alternative to the vernier kind; they show the reading directly.
main metric scale
two-hundredths of a mm
FIG. 1.4 Measuring using a vernier callipers 19 12 divisions
FIG. 1.5 Digital callipers show the reading directly Circular vernier scales
In general, vernier scales consist of a fixed scale and a secondary scale divided into smaller graduations. If the fixed scale is circular and divided into 360 degrees, it can be used to measure angles, as in a spectrometer (see Chapter 18).
For example, in Fig. 1.6, the main scale is read as between 19° and 20°. The secondary scale division that lines up closest is the 8th division (0.8°). This gives a total measurement of 19.8°.
You may now complete Exercise 1A (page 6). Graphs and proportionality
In physics experiments, you will often need to draw graphs of your results and develop conclusions based on them. The shape of a graph can tell you about the relationship between the variables you are testing in your experiment.
LEAVING CERTIFICATE PHYSICS 5
FIG. 1.6 Circular vernier scales can be used to measure angles
