. The principles of physics. mpared, it isonly necessary to obtain deflections with each current sepa-rately, and compare the tangents of the angles. 468. Ammeter. — Now if the value of each division of the 1 It is to be borne in mind that tbe formula C = K tan S measures the current electro-magnetic units and not in amperes ; and that 1 unit is equal to10 amperes. AMMETER. 499 scale be found by multiplying the number indicating thetangent of the angle of deflection by 10 K, and these resultsbe placed upon the scale in place of degree numbers, we shallhave a direct-reading ampe
. The principles of physics. mpared, it isonly necessary to obtain deflections with each current sepa-rately, and compare the tangents of the angles. 468. Ammeter. — Now if the value of each division of the 1 It is to be borne in mind that tbe formula C = K tan S measures the current electro-magnetic units and not in amperes ; and that 1 unit is equal to10 amperes. AMMETER. 499 scale be found by multiplying the number indicating thetangent of the angle of deflection by 10 K, and these resultsbe placed upon the scale in place of degree numbers, we shallhave a direct-reading ampere-meter (ammeter). There is agreat variety of ammeters in use, for a description of whichthe student is referred either to technical works on the sub-ject or to the inventors themselves. We shall consider only one other form, that called the(Kohlrausch) solenoid ammeter, selecting this because of itssimplicity. In Kg. 388, a is a helix of thick wire, 6 is a softiron tube which serves as a core, suspended by a light spring. I T I 1 h r d 1 m 1 i i 1 E 1 OOP 1 dl A 0 Fig. 388. c. The core carries a marker y; / is merely a wooden guide-rod for the tubular core. The action of this ammeter dependsupon the principle that when an insulated wire is wound intoa helix (called also a solenoid), and a current is passedthrough the wire, an iron rod or tube placed at the openingwill be drawn into the helix with a force increasing with the 500 ETHBK DYNAMICS. strength of the current. This force acting against the elasticforce of the spring may be measured in the same manner asweight by a spring balance. Now as the current strengthbears a definite relation to the force, the instrument caneasily be calibrated in amperes. Section IX. RESISTANCE OF CONDUCTORS. 469. External and internal resistance. — For conveniencethe resistance of an electric circuit is divided into two parts,the external and the internal. External resistance includesall the resistance of a circuit except that of the gener
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
