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CIRCUITS
6-1
Electrical Flow

Electric current is electric charge that flows. However
charge doesn’t flow continuously through a material
unless the material forms a closed path, or loop. A
Circuit is a closed path through which a continuous
charge can flow.
Parts of a Circuits




Voltage Source
Conductor
Switch
Electrical Device
Example
Voltage Sources

In a circuit this provides electrical potential for the
charge to flow. Batteries are often the voltage
sources in a circuit.
Conductor

A circuit must be a closed path in order for charge
to flow. In order to do so there must be a conductor,
such as a wire, that forms a connection from the
voltage sources to the electrical device and back
Switch

A switch is a part of a circuit designed to break the
closed path of charge. When a switch is open, it
produces a gap in the circuit so that the charge
cannot flow.
Electrical Device

An electrical device is any part of the circuit that
changes electrical energy into another form of
energy. A resistor is an electrical device that slows
the flow of charge in a circuit. When the charge is
slowed some energy is converted to light or heat. A
light bulb is an example of a resistor.
Circuit Diagrams

Symbols are used to represent the parts of a circuit.
The circuit diagrams below show the circuit of the
previous picture in both open and closed positions.
Open and Closed Circuits


Current in a circuit is similar to water running
through a hose. However, there is one difference
between water and electrical flow. If you cut the
hose, the water continues to flow. However if you cut
a wire, the charge stops flowing.
Batteries have connections at both ends so that
charge can flow a closed path to and from the
battery.
Open and Closed Circuits cont

Switches work by opening and closing the circuit. A
switch that is on closes the circuit and allows the
charges to flow. A switch that is off opens the circuit
and stops the current.
Short Circuits

A short circuit is an unintended path connecting one
part of a circuit with another. The current in a short
circuit flows a closed path, but the path is not the
one it was intended to follow.
 Pg
174
Grounding

In many electrical plugs one prong is dedicated to
being a ground. If there is a short circuit the charge
might flow dangerously to the outside the shell of
the appliance. However a ground wire, the current
will flow safely into the ground, along either a
buried rod or a cold water pipe.
Fuses


Are a safety device designed to open a circuit
when there is too much current running in it. Usually
consists of a thin strip of metal that is inserted into
the circuit. If a fuse is blown the fuse must be
replaced to close the circuit.
Other safety devices

Modern homes do not use fuses. Instead they use
other devices known as circuit breakers. These do
not have to be replaced each time they open the
circuit. When a short circuit or overload occurs a
switch is flipped causing the circuit to open.
Other safety devices cont.

Another safety device is a Ground-fault Circuit
Interrupter outlet (GFCI). These are required in
places where exposure to water is common. A tiny
circuit inside the GFCI outlet monitors the current
going out and coming in. If current flows through an
unintended path the circuit stops the current.
Assignment

Pg 177 problems 1-5