. A text book of physics, for the use of students of science and engineering . adingsmav be taken to one hundredth of amillimetre. In Fig. 17 the scales areshown set at 7-47 mm. In micrometers graduated in theBritish system the screw has usually40 threads per inch ; the barrel scale Ashows inches divided into fortieths;the thimble scale has 25 the instrument reads to _i_xTV = 0-001 the point of the screw is in con-tact with the abutment, the scalesshould read zero ; if this is not so, the reading should be noted, andapplied as a correction to subsequent measurements. Ex
. A text book of physics, for the use of students of science and engineering . adingsmav be taken to one hundredth of amillimetre. In Fig. 17 the scales areshown set at 7-47 mm. In micrometers graduated in theBritish system the screw has usually40 threads per inch ; the barrel scale Ashows inches divided into fortieths;the thimble scale has 25 the instrument reads to _i_xTV = 0-001 the point of the screw is in con-tact with the abutment, the scalesshould read zero ; if this is not so, the reading should be noted, andapplied as a correction to subsequent measurements. Expt. 4.—Use of vernier calipers and micrometers. Take again thebodies used in Expt. 2. Remeasure them, using the vernier calipers and the micrometer. Calculate the volumes fromthese dimensions, and compare the results withthose obtained by the methods employed inExpt. 2. The student is here reminded that theresults of calculations should not contain anumber of significant figures greater than is warranted by theaccuracy of the measurements. Thus it would be absurd to state. Fig. 16.—Micrometer. *S\ A s-o i i j i i Fig. 17.—Micrometer scales. 18 DYNAMICS CHAP. a result of 32146934 c\ibic millimetres when the instrument employedreads to 0-01 mm. only. Four significant figures are sufficient formost results ; the usual plan is to state one significant figure in excessof those of which the accuracy is undoubted ; for example, 32146may be taken to mean that 3214 is of guaranteed accuracy, butthat there is doubt regarding the last significant figure 6. Spherometer.—An ordinary type of spherometer is shown in A small stool A has three pointed legs B, C and D arranged at the corners of an equilateral triangle. Amicrometer screw E is fitted at thecentre of the circumscribed circle ofthe triangle, and is pointed at its lowerend. F is a graduated circular platefixed to the screw ; there is a milledhead at G for convenience in rotatingthe screw. A scale H is fixed to
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishe, booksubjectphysics
