Page 40 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

Conductors and Insulators E 1

Now consider a simple ‘PO5
circuit consisting of a
resistor, an inductor, and a
switch. Initially the switch
is in the OPEN (OFF)
position, the inductor VIND
voltage v,,,, is at ~po5 volts,
and no current is flowing
(Figure 3-14).
As the inductor is
formed from a piece of switch
conducting wire, lone
0
Volts
might expect that closing I __c__. 0 Volts
the switch at time To (b) At time To
would immediately cause (a) Switch is open switch is closed
v,,, to drop to 0 volts;
however, when the switch Figure 3-1 4. Resistor-inductor-switch c i ~ ~ ~ ~ t
is CLOSED (turned ON) and
current begins to flow, the inductor’s electromagnetic field starts to form.
As the field grows in strength, the lines of flux are pushed out from the center,
and in the process they cut through the loops of wire forming the coil. This has
ct as moving a conductor through an electromagnetic field and a
voltage differential is created between the ends of the coil. This generated
voltage is such that it attempts to oppose the changes causing it (Figure 3-15).
This effect is called inductance, the official unit of which is the henry.13
As time progresses, the coil’s inductance is overcome and its electromagnetic
field is fully established. Thus, by the time we’ll call TSTABLE, the inductor
appears little different from any other piece of wire in the circuit (except for its
concentrated electromagnetic field). This will remain the case until some new
event occurs to disturb the circuit-for example, opening the switch again.
Inductors are typically formed by coiling a wire around a ferromagnetic rod.
When you strike a musical tuning fork, it rings with a certain frequency

13 ‘The term henry is named after the American inventor Joseph Henry, who discovered inductance
in 1832.