Page 44 - Physics

Physics for Secondary Schools

distance between two consecutive threads
of the screw. This is called the pitch of 35
the screw. If the pitch of the screw of the 5 30
micrometre is 0.5 mm, then the thimble
scale has 50 equal divisions. Otherwise, it 25
has 100 divisions when the pitch is 1.0 mm. 20

This means that when the thimble makes Figure 2.16: Reading a micrometre screw
a complete turn, the spindle moves either gauge
forward or backward a distance of 0.5 mm
or 1.0 mm respectively along the sleeve. 4. Read and note down the value on the
When the spindle is completely closed onto thimble that is just below the reference
the anvil, the thimble edge aligns with the line on the sleeve. This value is to the
nearest hundredth of a millimetre (0.28
zero mark on the sleeve scale. The thimble mm for Figure 2.16).

also has its zero-mark lying on the central
line of the sleeve scale. Therefore, the gap 5. Add the values in steps 3 and 4.
Therefore, for Figure 2.16,
between the spindle and the anvil equals the
distance between the edge of the thimble Reading = Sleeve Scale Reading (SSR)
+ Thimble Scale Reading (TSR)
and the zero mark on the main scale.
= SSR + TSR

Measuring the diametre of a wire by = 7.50 mm + 0.28 mm = 7.78 mm
micrometre screw gauge
The following are procedures for measuring Task 2.4
the diametre of a wire using micrometre Diametre of a steel ball is measured
screw gauge. using a vernier calliper which has

1. Unscrew the thimble to create enough divisions of 0.1cm on its main scale
space to accommodate the wire between (MS) and 10 divisions of its vernier
the spindle and the anvil. scale (VS) match 9 divisions on the
2. Close the gap by rotating the thimble main scale. Three such measurements
clockwise. Screw the ratchet knob for a ball are given in the following
until it clicks so as to show the correct table.
setting. S/N MS (cm) VS division
3. Read and note down the value on 1. 0.5 8
the sleeve; that is the last mark must 2. 0.5 4
be visible to the left of the thimble. 3. 0.5 6
This value is to the nearest tenth of a If the zero error is -0.03 cm, calculate
millimetre. For example, in Figure 2.16, the average corrected diameter.
the value is 7.5 mm.

38
Student’s Book Form One

Physics Form 1 Final.indd 38 16/10/2024 20:55