REACTANCE AND FREQUENCY

Inductive reactance is one of two kinds of reactance. (The other kind will be dealt with in a little while.) In mathematical expressions, reactance is symbolized X. Inductive reactance is denoted X_L. If the frequency of an ac source is f (in hertz) and the inductance of a coil is L (in henrys), then the inductive reactance X_L (in ohms) is
X_L = 2πfL ≈ 6.2832fL
This same formula applies if the frequency f is in kilohertz and the inductance
L is in millihenrys. It also applies if f is in megahertz and L is in microhenrys. Remember that if frequency is in thousands, inductance must be in thousandths, and if frequency is in millions, inductance must be in millionths.
Inductive reactance increases linearly with increasing ac frequency. This means that the function of XL versus f is a straight line when graphed. Inductive reactance also increases linearly with inductance. Therefore, the function of X_L versus L also appears as a straight line on a graph. The value of X_L is directly proportional to f; X_L is also directly proportional to L.
These relationships are graphed, in relative form, in Fig. 1.

Fig. 1. Inductive reactance is directly proportional to inductance, as well as to frequency.