文档介绍：: .
modeled as an ideal source that puts out a constant voltage, VB, no matter what
amount of current, i, is drawn. The wires are considered to be perfect conductors that
offer no resistance to current flow. The switch is assumed to be open or closed. There
is no arcing of current across the gap when the switch is opened, nor is there any
bounce to the switch as it makes contact on closure. The light bulb is modeled as a
simple resistor, R, that never changes its value, no matter how hot it becomes or how
much current is flowing through
it.

Fig. 1-1 (a) A simple circuit
(b) An idealized representation
of the circuit

For most purposes, the idealized model shown in Fig. 1-1b is an adequate
representation of the circuit; that is, our prediction of the current that will flow
through the bulb whenever the switch is closed will be sufficiently accurate that we
can consider the problem solved. There may be times, however, when the model is
inadequate. The battery voltage, for example, may drop as more and more current is
drawn, or as the battery ages. ———— The light bulb’s resistance may change as it
heats up, and the filament may have a bit of inductance and capacitance associated
with it as well as resistance so that when the switch is closed, the current may not
jump instantaneously from zero to some final, steady state value. The wires may beundersized, and some of the power delivered by the battery may be lost in the wires
before it reaches the load. These subtle effects may or may not be important,
depending on what we are trying to find out and how accurately we must be able to
predict the performance of the circuit. If we decide they are important, we can always
change the model as necessary and then proceed with the analysis. The point here is
simple. The combinations of resistors, capacit