To measure the diameter of a wire with the help of a screw gauge we follow the following steps —
- Find the least count and the zero error of the screw gauge.
- Turn the ratchet anticlockwise, to obtain a gap between stud A and the flat end B. Place the wire in the gap between stud A and the flat end B. Then turn the ratchet clockwise to hold the given wire gently between the stud A and the flat end B of the screw.
- Note the main scale reading.
- Note that division p of the circular scale coincides with the baseline of the main scale. This circular scale division p when multiplied by the least count, gives the circular scale reading i.e., Circular scale reading = p x L.C.
- Add the circular scale reading to the main scale reading to obtain the total reading (i.e., the observed diameter of the wire).
- Repeat it by keeping the wire in a perpendicular direction. Take two more observations at different places of the wire and record them in a table.
Observations —
Pitch of the screw = ……… cm
Total number of divisions on the circular scale (n) = ………..
L.C. of screw gauge = Pitch / Total no. of circular scale div =
Zero error = ……. cm
| S No. | The main scale reading (in cm) | Circular scale reading b = number of divisions of circular scale in line with the baseline, p × L.C. (in cm) | Observed diameter = a + b (in cm) |
|---|---|---|---|
| (1) (i) in one direction (ii) in perpendicular direction |
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| (2) (i) (ii) |
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| (3) (i) (ii) |
Mean observed length = ……… cm
From the mean observed length, subtract zero error, if any, with its proper sign to obtain the true measurement of the length of the given project.
Thus we get,
Thus,
Observed diameter = main scale reading + (circular scale division p coinciding the coinciding the baseline of main scale x least count).
True diameter = observed diameter – zero error (with sign)
