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Series and Parallel Circuits
Chapter 9.1
Series Circuits
 “Charges with ONE path to follow”
Example:
Christmas Lights!
Series Circuits
 If there is a break in one part of the circuit ...
NONE OF THE CIRCUIT WILL WORK!
Series Circuit
 The total voltage in a series circuit is spread across the
loads:
 a voltage drop occurs at each load where some of the total
voltage is “lost”  i.e. transferred to other forms of energy
Voltage
here = 4V
Series Circuit
 The current in any part of the series circuit is the same ....
since there is only one path for the current to travel
Series Circuits
 Resistance reduces or slows the flow of electrons in a circuit.
 When more loads are added to a series circuit:
 the total resistance in the circuit increases
 the current decreases
Parallel Circuits
 A parallel circuit has multiple paths for current to follow.
 If there is a break in one part of the circuit, the current in
that part of the circuit would stop.
Parallel Circuits
 The voltage in a parallel
circuit is the same
throughout.
Parallel Circuits
 The current in a parallel circuit is divided among the
different pathways that branch off.
• A junction point
is where a circuit
(and the current!)
divides into
multiple paths or
where multiple
paths combine
Parallel Circuits
 When loads are added to a parallel circuit, the total
resistance is decreased
 This occurs because more loads also means more paths and
more paths creates more routes for the current to flow,
which actually reduces the overall resistance
 This would also cause the total current to increase.
Comparing Series and Parallel Circuits
 Series Circuit in a DVD Player
• Remember in a series
circuit, if one
component ‘breaks’,
then none of it works...
• If the player stops
being able to read a
DVD, is it necessary for
the circuit component
that works the picture
and sound to function?
• No....
Comparing Series and Parallel Circuits
 Parallel Circuit in a House
• Remember in a
parallel circuit, if one
component ‘breaks’,
then ONLY that part
stops working...
• If the bedroom light
burns out, you would
NOT want the entire
circuit to stop...it IS
necessary for the other
components to still
function!
Comparing Series and Parallel Circuits
Flashlight – cells in series
 Batteries end to end
means :
↑ voltage = ↑ current
More light!!
 But... more current means
the batteries don’t last as
long and need to be
replaced more often
Lighthouse – cells in
parallel
 Batteries in parallel means
less voltage and current is
used so it:
LASTS LONGER!
 This means it requires less
maintenance which is
good if you’re an out-ofthe-way lighthouse...
Circuit Breakers
 A circuit breaker acts as a switch so it can cut off ALL power
coming into the house (main circuit breaker) or...
 It can break the circuit so current can no longer flow through
a specific (branch) circuit in your house
Circuit Breakers
 How does it work?
 Remember a house circuit is a parallel circuit with MANY loads
 In a parallel circuit, each additional load provides a new path
which decreases total resistance and increases total current
MORE CURRENT IN WIRES = MORE HEAT IN WIRES
TOO MANY LOADS AND = TOO MUCH HEAT
TOO MUCH CURRENT
FIRE!!
So...
Circuit Breakers
 When there is too much current (and heat!) in a circuit breaker, it
causes a bimetallic strip to bend, which breaks the connection and
stops the current BEFORE there is a fire...
 Once it’s cooled, you reset the switch and the circuit works again