Instruments Used in measuring length.
(i) Tape-measure: (Accurately measures length greater than 1metre:𝑙 > 1𝑚). E g length of a foot ball field, length of a plot of land etc.
(ii) Metre-rule 🙁 Accurately measures length greater than 12 centimetres but less than 1metre:12𝑐𝑚 < 𝑙 < 1𝑚). Eg length of a desk, breadth of a window, etc. A metre rule gives readings in cm to 1dp.
(iii) Vernier calipers or Slide calipers : Accurately measures length greater than 1cm but less than 12 cm:2.5cm < 𝑙 < 12 cm. E.g Internal and External diameters of test tubes and beakers, breadth of a metre rule.etc. A vernier caliper gives readings in cm to 2dp.
The distance between the jaws is after wards measured on an ordinary scale like a metre-rule.
How to read a vernier Caliper
Reading of vernier calipers,
- Record the reading on the main scale to two places in cm.
- Look along the Vernier scale carefully until you see
division on it which coincides with the main scale, this gives
the second decimal place.
What readings are represented in the diagram?
(iv) Micrometer screw gauge: (Accurately measures length less than 1centimetre: 1𝑚𝑚 < 𝑙 < 25𝑚𝑚). Eg Diameter of wires, Diameter of ball beairings and pendulum bob, etc.
A micrometer screw gauge gives readings in cm to 2dp.
Precautions taken when using a micrometer screw gauge
- The faces of the anvil and the spindle must be cleaned to remove dust so as to get accurate readings.
- The reading must be checked.