Tab Electronics Guide to Understanding Electricity ... - Sciences Club

372 Chapter Fifteen
implementing capacitors for coupling and bypass functions, and recognizing
the effects of reactive components on the phase of AC voltages
and currents. At this point, you will probably find it relatively easy to
solidify some of the more vague concepts into definite mathematical
terms and relationships.
I suggest that you read and study the information contained in this
chapter, and then go back to reexamine many of the circuits incorporating
capacitors and inductors in the previous chapters. This process will
help to not only clarify a few of the operational principles contained in
previous circuits but also drive home the points covered herein.
Inductive Reactance
As stated previously, capacitors and inductors are reactive components.
This means that they “react,” or oppose, changes in electrical variables.
For example, a capacitor opposes, or reacts, to a change in voltage. Inductors,
on the other hand, “react” to a change in current flow. This reactive
effect has a profound relationship to frequency.
As the frequency of the applied voltage to an inductor is increased,
the inductor’s opposition to AC current flow increases. This is because
the amount of energy capable of being stored in the inductor’s electromagnetic
field (its inductance value) remains constant, but the time period
of the applied AC voltage decreases. As the AC time period decreases,
less energy is required from the inductor’s electromagnetic field to
oppose voltage alternations. For example, it would take 10 times the energy
to oppose 100 volts for 10 seconds than it would to oppose the same
voltage for one second. The same principle applies with an increase in
the frequency (decrease in time period) of the applied AC. Another way
of stating this basic principle would be to say that the reactance of an
inductor increases with an increase in frequency.
This frequency-dependent opposition to AC current flow through an
inductor is called inductive reactance. Inductive reactance (X L
), as are
impedance (Z) and resistance (R), is measured in ohms. The equation for
calculating inductive reactance is
X L
2fL
This equation states that inductive reactance (in ohms) is equal to 6.28
(the approximate value of 2) times frequency times the inductance