TABLES 329, 330. 



TABLE 329. Electrical Resistance of Straight Wires with Alternating Currents 

 of Different Frequencies. 



297 



This table gives the ratio of the resistance of straight copper wires with alternating currents of 

 different frequencies to the value of the resistance with direct currents. 



Values between i.ooo and i.ooi are indicated by *i.ooi. 



The change of resistance of wires other than copper (iron wires excepted) may be calculated 

 from the above table, making use of the fact that the change of resistance is a function of the 

 argument / = 2irrf2n\ where r = radius of cross-section, = frequency, X = conductivity. 



If a given wire be wound into a solenoid, its resistance, at a given frequency, will be greater than 

 the values in the table, which apply to straight wires only. The resistance in this case is a com- 

 plicated function of the pitch and radius of the winding, the frequency, and the diameter of the 

 wire, and is found by experiment to be sometimes as much as twice the value for a straight wire. 



TABLE 330. Electrical Resistance for High Frequencies. 



For which the high frequency resistance will be less than i per cent greater than 

 direct current resistance. 



Advance wire is practically identical electrically with constantan, while for high resistance Ger- 

 man silver the values are nearly the same as for manganin. The column of the table under maxi- 

 mum current gives the approximate current which may be carried by the various sizes without 

 undue heating. The current capacity of the manganin is very nearly the same. 

 From Austin, Jour. Wash. Acad. of Sci. 2, p. 190, 1911. 



SMITHSONIAN TABLES. 



