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Circuits
Series vs Parallel
Electric Circuit
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Path of current flow
As electrons move through a circuit, they
transfer potential energy from the source to
the device (load)
Circuits must be a continuous path in order
for electrons to flow (closed circuit)
Any break in pathway stops electron flow
(open circuit)
Electrons flow from – to +
Schematic Diagrams
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Use symbols to show circuit
Series Circuit
Loads connected end to end
 Each Electrons have only one path to
travel
 electron must go through each load
before returning to the source
 Same amount of charge passes through
each resistor so I is same for all
 I is constant
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Different Resistors
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Current is constant throughout
 The V across each resistor will be different for
different resistors
 The total of the V of the circuit will be the sum
of the V of each resistor
V = V1 + V2 + V3
 The total resistance is the sum of the
resistances of each load
REQ = R1 + R2 + R3
About Series
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More resistance you add, greater the total
resistance, the less current through the circuit
 Series wiring is easy and doesn’t use much
wire
 One load out breaks circuit and it all goes out
 Total current is decreased by the addition of
loads
Parallel Circuit
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Current splits to separate branches
 Each electron travels through only one load
before returning to the source
 Only some of the electrons go through each
path so current is split between paths
 Total current is sum of currents through each
path
ITOT = I1 + I2 + I3
About Parallel
V is constant in parallel circuit
 Total resistance is actually smaller than
that of the individual resistors
 Requires more wiring
 Don’t all go out if one does
 No loss of brightness (V) across
resistors
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Example
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Two 100 Ω resistors are connected a) in
series and b) in parallel to a 24V
battery. What is the current through
each resistor and what is the equivalent
resistance of each circuit?