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Series and Parallel– Simple Circuits
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Series vs. Parallel circuits
• What happens when a light goes out in a string of
christmas light?
• What happens when a light bulb goes out in your
house?
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Look at the two circuits shown
A.
BRIGHTER
B.
DIMMER
What
do
happens
The
Series
we
Parallel
In circuit
call
other
ifare
Circuit
circuit
you
Circuit
circuit
Athe
bulb
the
unscrew
B?
A?
bulbs
stays
goesthe
out.
lit.
are
a
one
bulb
the
bulb
inbrightest.
circuit
in Circuit
B? A?
In
which
circuit
bulbs
brightest?
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Series Circuits
• When electrons have only
one path to follow (like a
single slide at a water
park)
• If a person stops the
current stops, if they close
the slide (open a switch)
the current will no longer
flow.
• A circuit with only one
path to follow is called a
Series Circuit.
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Voltage in a Series
• A battery loses all the voltage
it pushes around the circuit by
sharing it around all the loads
in the circuit.
• Think about when you walk
up 12 steps of ladder to a
slide. You lose all 12 steps as
you go down the slide, then
you get the push of the stairs
back up to the top.
• In a series circuit, the sum of
the voltages lost on the loads
equals the total voltage
supplied by the battery.
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Measuring voltage in a Series Circuit
For a series circuit, the sum of the voltages for each component
is equal
todo
theyou
voltage
across
the
orlocations
battery. shown.
Set
up
the
apparatus
as shown……
…then
What
record
notice
the voltages
about
the
atcell
the
readings?
V1 = V2 + V3
V1
Note: Voltmeters are
connected in parallel
V2
Voltmeter
Voltage
(V)
V1
V2
V3
1.5
0.75
0.75
V3
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Current in a Series Circuit
In a series circuit the current is the same
Set
up
theyou
circuit
shown
below……
…and
The
What
current
then
do
record
isnotice
the
the
same
about
current
for
the
each
using
readings?
ammeter.
an ammeter
wherever
you
measure
it.
in the places shown below.
When measuring current ammeters are always
placed in series.
A
A
A
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Current in a Series Circuit
• Current is shared
along each part of a
circuit evenly.
• Ex. like water flowing
through a hose. No
matter what part of the
hose you look at, the
current that will be
flowing will be the
same.
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Resistors in Series
• When you slide down a water slide if all of a
sudden there was no water and you slide down dry
plastic you would slow down (probably hurt a bit
too…)
• This is just like resistance, as people must slow
down riding the slide when they hit the dry bit,
there will be less people riding the slide per
minute. Think of resistors like the dry part,
slowing down electrons in a circuit, decreasing the
current (amount of electrons flowing past a certain
part of the wire per second).
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Resistors in Series
• When resistors are
placed in series in a
circuit, the total
resistance increases and
the total current
throughout the circuit
decreases.
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Parallel Circuits
• A closed circuit where there is more
than one path for electrons to flow
through is called a parallel circuit
• There are three possible paths,
electrons can flow to bulb 1, 2 or 3.
• If one bulb goes out, the other ones
will not be affected.
• Think about a waterslide park with
one slide closed. The kids can still
get to the bottom by taking another
slide.
• The part of a circuit where it braches
off is called a junction point
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Measuring voltage II
V1
For
..measure
parallel
circuit,
voltage
theat
Setado
up
thethe
apparatus
What
you
notice
about
the
voltage
locations
across
shown.
the
as
shown….
your
readings?
cell/battery is the same
as the voltage across
each branch.
V1 = V2 = V3
V2
V3
Voltmeter
Voltage
(V)
V1
V2
V3
1.5
1.5
1.5
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Measuring current II
For a parallel circuit, the current that leaves the cell or battery is the same
as
the
that
returns
to at
the
cellreadings?
or battery.shown.
The current does not get
…then
What
record
you
the
notice
current
about
the
the
locations
Setcurrent
updo
the
circuit
shown
below……
used up by a circuit, just the energy the electrons are carrying. Pathways
with less resistance will have more current flowing through.
A1 = A4
A1
Ammeter
Current
(A)
A1
A2
A3
A4
0.8
0.5
0.3
A4
A2
A3
0.8
The sum of the currents at a junction point of a
parallel circuit is the equal to the current that
leaves the junction point or battery.
A1 = A2 + A3 =A4
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• The total current entering a junction point must
Equal the sum of the current leaving the junction
point. Loads of different resistance will have
different currents.
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Resistors in Parallel
• When resistors are placed in parallel you
create another pathway so the overall
resistance is decreased.
• When the total resistance decrease what
happens to the current in the circuit?
– Think about I = V/R
– It increases!!!!
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Resistors in Parallel
• If you only have one
pathway, the resistance
will be higher than if
you have two
pathways.
• Therefore, the more
resistors you add in
parallel, the less total
resistance there is and
the more current will
flow.
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The Power of Electricity
Power = rate of change in energy or the rate at
which work is done or being transformed.
• The unit of energy is the Joule (J). One joule
(J) of energy transformed in one second (s) is
called a watt (W) of power.
• 1 Watt = 1 J/s
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Calculating Electrical Power
• Electrical power is the
rate of change in
electrical energy.
• What changes electrical
energy to other forms?
– Load (light bulb, stereo)
• Calculating Electrical
power of a device by
using:
P(power) = V x I
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Energy Consumption
• Power is the amount of
energy used over time.
• P = E/t
• Power = Energy/time
Switch around equation
• Energy = P x t
• Create another Triangle
• This power rating is usually seen
on electrical devices such as
blenders, hair dryers, computer
power supplies, and heaters.
E (J) = P(W) × t(s)
Energy (Joules) = Power
(Watt) × time (seconds)
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Large Units of Energy
• A joule is a very small
measure of energy.
• 1.0 joule = 1.0 watt X 1.0
second
• Large quantities of energy
are measured in kilowatt–
hours (kW•h)
1000 W = 1 kW
3600 s = 1 h
1.0 kW•h = 1.0 kW × 1.0 h
1.0 kW•h = 1000 W × 3600 s
1.0 kW•h = 3,600,000 J = 3600
kJ
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Cost of Electricity
• BC Hydro monitors the
electricity used in your
home by a meter that
measures the energy used in
kilowatt-hours
For example, if you used
1500 kW h and BC Hydro
costs $0.07 a kw h, how
much is your electric bill?
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Power Surges
• Why do we have power bars that we connect
our computers to?
• Surges can be caused by lightning, turning off
large electrical appliances and power company
“errors”
• Surge protectors absorb some of the extra
electricity and send the rest to ground
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