218 ELECTRICAL MACHINERY 



From these calculations we see that the result of increasing 

 the frequency in an inductive circuit is to decrease the 

 current, the power used, and the power factor. A decrease 

 in frequency produces the opposite effects. 



53. Capacity. Two conducting plates, separated by a 

 dielectric, constitute what is called a condenser. This 

 name is given to such an arrangement because it seems 

 to condense, or hold, the electricity which runs into it. 



Construction of a Condenser. An ordinary condenser 

 consists not of one pair of plates but of several hundred or 

 more plates of tin-foil, separated by sheets of a special 

 grade of paper which has been impregnated by some insu- 

 lating compound. Every other sheet of tin-foil is con- 

 nected together and these form one terminal of the con- 

 denser; the remaining sheets are connected together to 

 form the other terminal. 



Condenser in a C-C. Circuit. When a condenser is 

 connected to a c-c. line, there is an instantaneous rush of 

 current until the condenser is charged and then no more 

 current flows unless the voltage of the line changes. If 

 the condenser is disconnected from the line and its two 

 terminals connected together by a conductor, there is a 

 sudden rush of current through the wire and the condenser 

 becomes discharged. 



Charge and Discharge Current Curves. The charge and 

 discharge currents ordinarily last for only a small fraction 

 of a second; typical curves are shown in Fig. 130. The 

 full line curves represent the currents in a paraffine con- 

 denser and the dotted line curves those for a mica con- 

 denser. The substance which separates the metal plates 

 of a condenser is called the dielectric; the difference in the 

 shape of the two sets of curves in Fig. 130 is due to the 

 characteristics of the two different dielectrics, viz., paraffine 

 and mica. 



Condenser in an A-C. Circuit. Now if a condenser is 

 connected to a line of alternating e.m.f., there will be 



