Author: Hobart Mason

Publisher: Rarebooksclub.com

Published: 2013-09

Total Pages: 34

ISBN-13: 9781230025735

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1904 edition. Excerpt: ...MEASUBEMENT OF CAPACITY. 38. Measurement of Capacities--Whether the dielectric of a condenser is solid or fluid, the capacity is modified by conduction and by dielectric hysteresis, and is some function of the time of charging and the time between charging and measurement. Where these conditions are of any magnitude the capacity can be closely determined only by some method making use of rapid periodic charging and discharging. The direct conductivity of a condenser may be determined by the galvanometer as in ordinary insulation tests. Furthermore the capacity of the wires used in connecting up the condenser may be of such magnitude as compared to the capacity to be measured as to render it necessary to determine their capacity separately and subtract it from the observed capacity to give the true capacity of the condenser. In the electromagnetic system a capacity has the same dimension as the quotient of a time divided by a resistance, hence the suitable measurement of a time and a resistance will determine a capacity. If the time be measured in seconds and the resistance in c. g. s. units the capacity will be expressed in c. g. s. units, while if the time and resistance be measured in seconds and ohms respectively, the capacity is given in farads. An application of this principle is shown in Fig. 35, where x and y are the coils of a differential galvanometer, and T a tuning-fork contact maker charging and discharging the condenser h at a known frequency. The condenser charges at the battery pressure, and discharges through the coil y. Coil x is constantly excited by a shunt current. Now, if the resistances ab and be are so chosen that the galvanometer does not deflect, and if we let i?j = resistance of ab R2 = resistance of ac Bg =...