Page 43 - Physics

Measurement

A test tube is cylindrical in shape. This means that its diametre is the same throughout.
The readings obtained using the outside calliper jaws are equal in magnitude since the
test tube is almost uniform in shape.

In an experiment, it is always best to obtain many readings so as to obtain an average
result. Two or more readings offer an opportunity for the experimenter to compare and
identify any pattern.

Task 2.3

Collect a variety of objects such as books, pencils, beakers, test tubes and other
materials available at your physics laboratory. Use a vernier calliper to measure
the thicknesses of the collected objects. The depth, internal and external diameters
of the hollow objects should also be measured. Record your measurements in the

following table:
Object Dimension Main scale Vernier scale Actual reading
(cm) reading (cm) reading (cm) (cm)

A micrometre screw gauge
A micrometre screw gauge gives readings with better precision than the vernier calliper.
Measurement can be obtained to the nearest thousandth of a centimetre. This is an
accuracy of 0.001 cm. For this reason, it is usually used to measure the diameters of thin
objects like wires and ball bearings. The micrometre screw gauge has different parts,
as shown in Figure 2.15.

Anvil
Anvil Sleeve (with main scale)
Spindle
Spindle
Spindle
Ratchet
knob
Thimble (w
Thimble (with rotating ith rotating
vernier scale division)
vernier scale division)

Frame
Frame

Figure 2.15: Parts of the micrometre screw gauge

A micrometre screw gauge consists of main scale (sleeve) and thimble scale. The
main scale is marked in millimetres. The thimble scale is divided depending on the

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