630 



Popular Science Monthly 



the terminals of the condenser connected 

 together, as in Fig. 3, the charge will flow 

 out and will result in a current of short 

 duration. This current is at its maximum 

 when the terminals are first connected, 

 but it soon dies down to zero value. 



When a condenser is charged, the po- 

 tential difference at the terminals does not 

 instantly come to a maximum value; in 

 other words, a certain time elapses before 

 the condenser reaches full charge. This 

 apparent absorption is due to an action on 

 the dielectric surface. At discharge, a 

 certain time also passes before the pre- 

 vious charge is entirely removed; some of 

 the charge has been absorbed into the die- 

 lectric, which charge is called residual. A 

 condenser exhibiting this quality pos- 

 sesses residual absorption. Hence, the 

 actual capacity of a given condenser is 

 not definite, depending as it does upon the 



Condenser 



rig. 5 



With the battery removed and the circuit 

 made complete the chaige soon flows out 



amount of residual absorption and leakage. 



Condensers may be connected in par- 

 allel, as in Fig. 4, or in series, as shown in 

 Fig. 5. The combined capacity of two 

 condensers in parallel is equal to their 

 sum. If Ci and C2 are the capacities of 

 the two condensers illustrated diagram- 

 matically in Fig. 4, their combined capa- 

 city will equal C, -f C... This is true for 

 any number of condensers connected in 

 parallel; hence, if a number of condensers 

 are connected in parallel, their combined 

 capacity is equal to the sum of all the 

 capacities. 



The combined capacity of two con- 

 densers in series is equal to unity divided 

 by the sum of the reciprocals of the two 

 capacities; or, referring to P^'ig. 5: 



C = 



c, 



1 



c, + c. 



C, Co 



This rule applies to any number of con- 

 densers in series. 



Condensers are made by taking a large 

 number of tinfoil sheets and separating 

 them by alternate sheets of paraffined 

 paper, mica, or other insulating material. 

 The whole mass is pressed tightly to- 



ol. 



Tip 



C, 





D— 



fig. 4 



With condensers connected in parallel their 

 combined capacity is equal to their sum 



gether, one set of sheets being connected 

 with one terminal and the alternate set 

 with the other, as illustrated in Fig. 6. 

 It should especially be noted that no 

 electrical connection exists between the 

 sets of plates connected to the two termin- 

 als, since it is this property of inductivity 

 of the dielectric that enables the con- 

 denser to store up such an enormous 

 charge of electrical energy. 



The quantity of electricity held by the 

 condenser may be made greater by in- 

 creasing the charging E. M. F. and is 

 directly proportional to this E. M. F. 

 In addition, it is found that for a given 

 voltage, the quantity of electricity which 

 the plates will acquire depends upon their 

 size, their separation, and the dielectric or 

 insulation between them. The quantity 

 of electricity held by either plate of a 

 cliarged condenser, represented by Q, 

 may be written equal to the product EC, 



oTi TtO 



fig. 5 



Also if the condensers are connected in 

 series their combined value equals their sum 



where E is the charging E. M. F. and C is 

 a constant factor which takes into account 

 the construction of the condenser. This 

 factor C is known as the capacity of the 

 condenser. 



Thus, we may write, C = Q E, or the 

 capacity of a condenser is the quantity of 



