Quantcast Figure 19. Schematic symbols for inductors and
transformers  while coils having iron cores are usually designed
to operate at lower frequencies such as audio or power
frequencies. (2) Inductors having more than one winding are
usually called transformers. Their purpose is to physically
isolate one circuit from another, and to step up or step down
the voltage fed into the winding called the primary winding.
 Voltage for the circuit or then taken from the secondary
winding. (3) Samples of air-core and iron-core (magnetic-core)
inductors, and iron- core transformers are shown respectively in
A, B, and C of figure 18. (4) Examples of the schematic symbols
for these inductors can be seen in figure 19.  The air-core
transformer in sketch A are for passing radio frequencies.
 Sketch B shows an iron-core transformer.  Sketch C is the
schematic symbol for an iron-core inductor, and sketch D is the
symbol for an air-core inductor. Figure 19. Schematic symbols
for inductors and transformers. b. Capacitors. Cap