A direct current (DC) electrical circuit
consists of a source of DC electricity with a conducting
wire going from one of the source terminals to a set of
electrical devices and then back to the other terminal,
in a complete circuit. A DC circuit is necessary for DC
electricity to exist. DC circuits may be in series,
parallel or a combination. Understanding DC circuits is
important for learning about the more complex AC
circuits, like those used in the home.
Questions you may have include:
What does an electric circuit
What is a series circuit?
What is a parallel circuit?
If you take a continuous source of DC
electricity, such as a battery, and connect conducting
wires from the positive and negative poles of the
battery to an electrical device such as a light bulb,
you have formed an electric circuit.
The battery, bulb and switch inside a
flashlight form a DC circuit
In other words, the electricity flows in
a loop from one end of the battery (or source of
electricity) to the other end in a circuit. The concept
of electric circuits is the basis for our use of
One nice feature of an electrical
circuit is that you can install a switch in the circuit
to turn the power on or off when you want.
Note: Although electrons move from a
negative (-) area toward the positive (+), the
convention was established that electricity is
designation as moving from (+) to (-).
A DC circuit requires a source of power.
Typically, a battery is used to provide continuous DC
electricity. A DC generator is another source of energy.
Alternating current (AC) electricity can be modified
through a rectifier or adapter to create DC electricity.
The common adapter used for some of your small
DC-powered devices will transform 110V AC house current
into 12V DC current for your device.
The electricity moving through a wire or
other conductor consists of its voltage (V), current (I)
and resistance (R). The voltage or potential energy of a
source of electricity is measured in Volts. The current
of amount of electrons flowing through the wire is
measured in Amperes or Amps. The resistance or
electrical friction is measured in Ohms.
The wire and electrical devices must be
able to conduct electricity. Metal such as copper is a
good conductor of electricity and has a low resistance.
The tungsten filament in a light bulb conducts
electricity, but it has high resistance that causes it
to heat up and glow.
Series DC circuit
In an electrical circuit, several
electrical devices such as light bulbs can be placed in
a line or in series in the circuit between the positive
and negative poles of the battery. This is called a
Two light bulbs in a series circuit with
One problem with such an arrangement is
if one light bulb burns out, then it acts like a switch
and turns off the whole circuit.
Every device in a DC circuit--whether a
light bulb or electrical motor--can be represented by an
electrical resistance or resistor Usually, when drawing
a circuit diagram or schematic, you use certain symbols
for the battery and resistors.
Schematic of a DC circuit with three
resistor in series
Parallel DC circuit
Devices can also arranged in a parallel
configuration, such that if any bulbs go out, the
circuit is still intact. Not only is a parallel circuit
useful for holiday lighting, the electrical wiring in
homes is also in parallel. In this way lights and
appliances can be turned on and off at will. Otherwise
if you turned one light off--or one burned out--all the
other lights in the house would go off too.
bulbs in a parallel circuit
If either light bulb would go out, the
other would still shine. You could add other bulbs or
even appliances such as electric motors in parallel to
this circuit, and they would remain independent of each
Schematic of parallel DC circuit
You could also replace a bulb with a
series circuit of bulbs or add bulbs or devices in
series between parallel items. There are many
DC electrical circuits consist of a
source of DC electricity with a conducting wire going
from one of the terminals to a set of electrical devices
and then back to the other terminal, in a complete
circuit. DC circuits may be in series, parallel or some