Tables 414-llB. 



344 



TABLE 414. — Ratio of Altemating to Direct Current Resistances for Copper Wires. 



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

 to the value of the resistance with direct currents. 



Values between 1.000 and i.ooi are indicated by *i.ooi. 



The values are for wires having an assumed conductivity of 1.60 microhm-cms; for copper wires at room tempera- 

 tures the values are slightly less than as given in table. 



The change of resistance of wire other than copper (iron wires excepted) may be calculated from the above table 

 by taking it as proportional to dy/j/p where d = diameter,/ the frequency and p the resistivity. 



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 complicated 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 a.s much as 

 twice the value for a straight wire. 



TABLE 415. 



■ Maximum Diameter of Wires for High-frequency Altemating-to-direct-corrent 

 Resistance Ratio of 1.01. 



Frequency -^ 10^. . . 



Wave-length, meters 



Material. 



Copper 



Silver 



Gold 



Platinum 



Mercury 



Manganin.. . . 

 Constantan. . . 

 German silver , 



Graphite 



Carbon 



Iron fi s= 1000 

 M = 500.. 

 p, = 100.. 



Diameter in centimeters. 



0.0065 

 0.0063 

 0.0077 

 0.0205 

 0.0483 

 0.0325 

 0.034s 



0.03S4 

 o. 140 

 o. 292 



0.00048 

 0.00068 

 0.00152 



Bureau of Standards Circular 74, Radio Instruments and Measurements, 1918. 

 Smithsonian Tables. 



