appexdixa - Appendix A Measuring Techniques 1 Introduction...

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A Page 1 Measuring Techniques Appendix A A 1) Introduction: Every experiment in the elementary laboratory involves measurement. The kind of measurement will depend on the particular experiment, but there are certain basic measurements which are common to many different experiments.The following notes are intended to be a guide to the correct use of some common laboratory instruments and to suggest good measuring techniques. Special instruments used in some of the Frst year experiments are discussed in detail in the notes on those particular experiments. 2) Measurement of Length: In the elementary laboratory the length to be measured may be any distance between a small fraction of a millimeter and several meters. It is neither convenient, nor generally possible to use the same kind of instrument for the whole of this range. 2.1) Meter Stick: ±or distances greater than about 10 cm a meter stick is useful. The meter stick is divided into 1000 parts. These millimeter divisions are reliable to within ² l.0 mm if care is taken to avoid parallax errors (see discussion of errors). 2.2) Vernier Calipers: ±or distances between about 1 cm and 10 cm vernier calipers are used, (or some device with an attached vernier scale such as a traveling microscope). The vernier scale, as shown in Fgure (1), is an auxiliary scale which makes it possible to interpolate between the smallest divisions of the main scale, a process which cannot be performed with reliability by eye. 0 1 2 1 2 3 4 5 3 4 5 6 7 8 9 10 11 12 13 14 cm 0 1 2 3 4 5 6 7 8 9 0 0.05 mm 0 4 8 1/128 in in Figure (1) The vernier caliper
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A Page 2 The most common vernier scale has ten divisions in the same distance as nine divisions of the main scale. Each vernier division is therefore 0.9 of the main division. Vernier scales also exist with different ratios (see Fgure (2) for example). The same sort of arguments will apply using twentieths instead of tenths. If the vernier scale were moved to the right by 0.1 of a division the 1’ mark would line up with the 1 on the main
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appexdixa - Appendix A Measuring Techniques 1 Introduction...

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