Hawkins Electrical Guide v. 05 (of 10) / Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications

by N. Hawkins

The period of greatest rate of change is that at which cos φ has the greatest value, and the maximum value of a cosine is when the arc has a value of zero degrees or of 180 degrees, its value corresponding, being 1. (See fig. 1,037, page [1,068].)

The pressure due to inductance is equal to the product of the rate of change by the inductance; that is, calling the inductance L, the pressure due to it at the point of maximum value or

E_max = 2πfI_max × L (1)

Now by Ohm's law

E_max = RI_max (2)

for a current I_max, hence substituting equation (2) in equation (1)

RI_max = 2πfI_max × L

from which, dividing both sides by I_max, and using X_i for R

X_i = 2πfL (3)

which is the ohmic equivalent of inductance.