Circuit Types
DC Circuits
•
Identifying features:
o
Constant inputs: the voltages of independent voltage sources and currents of
independent current sources are all constant.
o
The circuit does not contain any switches.
•
All voltages and currents in a dc circuit are constant.
•
Capacitors act like open circuits and inductors act like short circuits.
Example:
Determine the current,
, and voltage,
( )
i t
( )
v t
, for this circuit.
Solution:
This is a dc circuit so the capacitor acts like an open circuit. The capacitor voltage,
, is the
voltage across that open circuit. The inductor acts like a short circuit. The inductor current,
( )
v t
( )
i t
,
is the current in that short circuit. Here’s the circuit after replacing the capacitor by an open
circuit and replacing the inductor by a short circuit:
Ohm’s law gives
( )
30
2.5 A
8
4
i t
=
=
+
and
( )
( )
(
)
4
4 2.5
10
v t
i t
=
=
=
V
1

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