CHAPTER V. 

 EFFECT OF CAPACITY. 



Capacity in an Alternating Circuit. All insulated con- 

 ductors have the property of being able to hold electricity 

 in its static form. When an insulated conductor is connected 

 to a source having a different potential, electricity will flow 

 to or from it until its potential is the same as that of the source. 

 The amount of electricity held by a conductor when its 

 potential is unity is called its capacity. Hence a conductor 

 has a capacity equal to unity when one unit of quantity of 

 electricity raises it to a potential of unity. 



The practical unit of capacity is the Farad. 



The unity of quantity of electricity is the Coulomb, and 

 is the quantity which is transmitted by a current of 1 ampere 

 in 1 second. 



Thus the charge of a condenser = number of coulombs 

 which have flowed into it = number of amperes x duration of 

 flow in seconds. 



A1 amount of charge amperes x seconds 



Also capacity - = 



potential due to charge volts 



The Farad being too large to correspond to the dimen- 

 sions of capacities occurring in practice, the microfarad, i.e., 

 one-millionth of a Farad, is usually employed. 



The capacity of a conductor depends on its size and shape 

 and upon its surroundings. 



A condenser may be any conductor having an appreciable 

 capacity, although it usually denotes a special piece of 

 apparatus consisting of thin sheets of metal separated by 

 insulating material, alternate plates being connected together 

 respectively to two terminals, so as to form two conductors of 

 very large surface separated by a very thin layer of insulation. 

 A condenser of this kind when connected to opposite poles of a 

 generator will take considerable charges on the two sets of 

 conducting plates, i.e., the generator will supply a certain 

 quantity of electricity, so as to charge the condenser. If the 

 generator supplies alternating current, the charges given to 

 the condenser plates will be alternatively positive and negative, 

 and there will thus be an alternating flow of electricity 



