Series versus Parallel Circuits
The Ultimate Battle!
KEY POINTS
NEW VOCABULARY:
–Resistance
–Voltage
–Ohm’s Law
RESISTANCE
RESISTANCE = the tendency for a
material to oppose the flow of electrons,
changing electrical energy into thermal
energy and light.
All materials have some electrical
resistance.
Resistance is measured in Ohms (W)
RESISTANCE
Examples:
1) Lightbulb
-Electrons flow through the filament of the lightbulb
and bump into the metal atoms that make up the
filament.
-Some of the electrical energy from the bumps turns
into thermal energy.
-Eventually the metal filament gets hot enough to glow,
making the lightbulb light up!
-Electric current loses energy as it moves through the
filament because the filament tries to stop the flow
of electrons (HIGH RESISTANCE!!!)
RESISTANCE
Examples:
2) Copper wiring
-Excellent to use in houses because it
has low resistance to the flow of electrons
-Less electrical energy is converted to
thermal energy so there is more electrical
energy to power the house!
(LOW RESISTANCE)
SAVE ENERGY! USE COPPER WIRES! 
Factors that affect resistance…
SIZE OF WIRE
– Electrons move more efficiently through thick
wires
(Thin wires have more resistance!)
-The longer the wire the higher the resistance!
TEMPERATURE
-High temperatures are also linked with high
resistance
VOLTAGE
Just like water flows from high to
low levels, electrical charges do
that too!
Voltage is like an electrical pressure that
pushes charges from high to low levels!
Voltage is measured in volts (V)
Ohm’s Law
There is a relationship between current,
voltage, and resistance.
– Current = I and is measured in amps (A)
– Voltage = V and is measured in volts (V)
– Resistance = R and is measured in ohms (W)
Current = voltage
resistance
V = IR
I=V/R
KEY POINTS
Anything that is plugged into an outlet requires electrical
energy!
That energy is moved around in CIRCUITS!
EX: Hair dryer
1. The dryer has to be plugged into the outlet to operate.
2. A generator at the power plant produces a voltage difference
across the outlet that makes charges move when the circuit is
complete.
3. The dryer and the house have wires that carry the current.
4. The dryer turns the electrical energy into thermal and mechanical
energy.
5. You break the path of current in the circuit when you turn off the
dryer or unplug it.
The Snowman Robber!
Types of Circuits!
Two types of
circuits:
–SERIES
–PARALLEL
SERIES CIRCUIT
Current flows through ONE loop!
The parts of a series circuit are wired one
after another.
The amount of current and voltage are the
same through every part.
When any part is disconnected, no current
flows and the entire circuit goes out!
Also called an OPEN CIRCUIT!
SERIES CIRCUIT
Examples:
–Flashlights
–Holiday lights
THINK, PAIR, SHARE…
Where would a series circuit be
inconvenient? Why?
SERIES CIRCUIT
SERIES CIRCUIT
SERIES CIRCUIT
PARALLEL CIRCUITS
Parallel circuits have 2 or more branches
for current to move through.
The voltage is the same in each branch of
the circuit, but more current flows through
branches that have lower resistance.
Advantages to Parallel Circuits…
When one part is disconnected, the current
still flows through the other branches.
Houses, cars, and most electrical systems
use parallel wiring.
THINK, PAIR, SHARE…
Why do you think houses use parallel
circuits?
Parallel Circuit
In a parallel circuit the
current flow splits up
and goes to different
parts of the circuit. If
one bulb or appliance
goes out, the rest stay
on. All bulbs are
equally bright.
PARALLEL CIRCUITS
PARALLEL CIRCUITS
COMPARE/CONTRAST
SERIES
– One loop of current
– Same voltage
everywhere
– Same current
everywhere
– If one part is
disconnected the
whole circuit goes out
– Used in lightbulbs!
PARALLEL
– 2 or more branches of
current
– Same voltage
everywhere
– Current changes
based on resistance
– If one part is
disconnected, the
circuit still carries
electricity to the other
branches
– Used in houses and
cars!
COMPARE/CONTRAST