Publisher's Synopsis
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1891 edition. Excerpt: ... CHAPTER III. Resistance And Conductance. Resistance Of Different Conductors Of The Same Material. Conductors are generally circular in section. Hence they vary in section with the square of their diameters. The rule for the resistance of conductors is as follows: Rule 13. The resistance of conductors of identical material varies inversely as their section, or if of circular section inversely as the squares of their diameters, and directly as their lengths. Example. 1. A wire a, is 30 mils in diameter and 320 feet long; another b, is 28 mils in diameter and 315 feet long. What are their relative resistances? Solution: Calling the resistances Ra: Rb we would have the inverse proportion if they were of equal lengths Rb: Ra:: 302: 282 or as 900: 784. Were they of equal diameter the direct proportion would hold for their lengths: R" Ra:: 315: 320. Combining the two by multiplication we have the compound proportion Rb: Ra:: 900 X 315: 784 X 320 or as 283,500: 250,880, or as 28: 25 nearly. The combined proportions could have been originally expressed as a compound proportion thus: Rb: Ra:: 302 X 315: 282 X 320. For wires of equal resistance the following is given. Rule 14. The length of one wire multiplied by the square of the diameter of the other wire must equal the square of its own diameter multiplied by the length of the other if their resistances are equal. Or multiply the length of the first wire by the square of the diameter of the second. This divided by the length of the second will give the square of the diameter of the first wire; or divided by the square of the diameter of the first will give the length of the second. Examples. 1. There are three wires, a is 2 mils, b is 3 mils, and c is 4 mils in diameter; what...
