Parallel Circuits
8 Note Boxes
Box #1
Quick Review
The electrons that move
to make electricity come
mostly from the wires in
the circuit, not the battery.
Metals are
conductors
because their electrons
can move.
Introduction
There are two network configurations – series
and parallel.
Last class we covered a series network.
 In this lesson we will cover the parallel circuit
and all the methods and laws associated with it.
Do You Remember?
What did we say was the biggest DISADVANTAGE
of using a series circuit?
Box #2-3 notes
Parallel
Branching Out
circuits have independent paths.
We call these independent paths “branches”.
Box #2-Con’t
Junction:
Junctions
Where the branches join or split
B1
B2
B3
B4
Box #3
Parallel Circuit Advantage
In
a parallel circuit, each device operates
independent of the other devices.

A break in any one path does not interrupt
the flow of charge in the other paths.
Independent Paths
Which one?
Which switch, if
opened, will cause
the light bulb to
stop glowing?
Why?
Which circuit is built so that if one light bulb
goes out, the other three light bulbs will
continue to glow?
Box #42 notes
 The
Voltage in Parallel Circuits
batteries are typically in series with one another.
 The total voltage therefore is found by adding up each
individual battery.
 The total voltage going across each branch is the same.
Box #4-Con’t
That was Easy…
Now
here’s is where things start to change from a
series circuit
The
total current divides among the parallel
branches
Huh?
Remember Ohm’s Law?
Ohms’s Law
(Amps)
(volts)
(ohms)
Comparing and Contrasting
Box #5Technically 2 Series vs Parallel
notes
If they’re all
in a row (series), you just add them
up and go!
If they have
a different road (parallel), take the
time to break the code.
Current in Parallel Circuits
Resistance
in
Parallel
Circuits
Box #6-2 notes
From
the battery’s perspective, the overall
resistance of the circuit is decreased.
This
means the overall resistance of the circuit is
less than the resistance of any one of the
branches.
Resistance in Parallel Circuits
think!
What happens to the light intensity of each lamp in a parallel circuit when
more lamps are added in parallel to the circuit?
Parallel Circuits
think!
What happens to the light intensity of each lamp in a parallel circuit when
more lamps are added in parallel to the circuit?
Answer:
The light intensity for each lamp is unchanged as other lamps are introduced
(or removed). Although changes of resistance and current occur for the
circuit as a whole, no changes occur in any individual branch in the circuit.
Box #6Con’t
Parallel Resistors
 For resistors in parallel, the total resistance is
determined from
Ready to rip your hair out yet?
There IS an
easier way…
Box #7
Circuit Overload
To prevent
overloading in
circuits, fuses or
circuit breakers are
connected in series
along the supply
line.
Box #8-2 notes
 When
Brain Break-Fuses
you blow a fuse, what does that
mean?
 Electricity through a circuit causes heat.
 Fuses melt (or break) when too much
current passes through it; they must be
replaced.
 This protects expensive electronic
equipment.
Box #8-Con’t
Circuit Breakers
Circuit Breakers
protect against
too much current
like fuses, but
can be reset.