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9.1 Series and Parallel Circuits
Pg. 306
People here have multiple paths to follow
Series Circuits
• Voltage decreases as electrons pass through each load
• Voltages across each of the loads adds up to the voltage
supplied by the source.
• There’s only one path to follow
• Current is constant throughout the circuit
• Resistance of resistors increases when in series
- like more speed bumps in a row
Parallel Circuits
• Voltage is the same across each load
• There’s more than one path to follow
• Current varies between each pathway, depending on the
resistance of the path, but still adds to the total current supplied
by the source.
• Resistance decreases with each added resistor
• New pathway created thus lowering the total resistance
• Junction point is where a circuit divides into multiple paths
– The total current entering
a junction point must equal
the sum of the current leaving
the junction point
Find the unknown Voltage (V) and the
Current (A) in each of the following
circuit diagrams.
Voltage = 10.0 V
Current = 3.0 A
Voltage = 12.0 V
Current = 4.0 A
COMPARING SERIES & PARALLEL CIRCUITS
SERIES
CIRCUIT
PARALLEL CIRCUIT
# of paths electricity can follow
One
More than one
Current throughout the circuit
Equal
Lower between
junction points
Voltage of loads in the circuit
Can vary
All the same
Effect of adding a second resistor on
total resistance
Increases
Decreases
Effect of adding a second resistor on
current
Decreases
Increases
DRAWING PARALLEL & SERIES
CIRCUITS
•Draw a circuit diagram consisting of
a 9.0 V battery, an ammeter, and a 25
 resistor in series. Include a
voltmeter that is measuring the
potential difference
across the resistor.
•Draw a circuit diagram consisting of
a battery made up of two 1.5 V cells,
one closed switch, two lamps, and
an ammeter in series. Show the
direction in which the current flows.
•Draw a circuit diagram consisting
of a battery made up of four 1.5 V
cells, one closed switch, one lamp,
two 0.50  resistors in series, and a
voltmeter. Show the direction in which
the current flows.
MORE PRACTICE DRAWING
PARALLEL & SERIES CIRCUITS
Draw a series circuit consisting of:
12 V electrical source
open switch
two light bulbs
10  resistor
Draw a parallel circuit consisting of:
9.0 V electrical source
open switch
three 5.0  resistors
Draw a circuit consisting of:
three 1.5 V cells connected in parallel
open switch
two light bulbs connected in series
two 15  resistors connected in parallel
INTERPRETING CIRCUIT DIAGRAMS
Describe what will happen in the circuit shown above if…
(a) the switch is closed
(b) the switch is closed and the first bulb is removed
(c) the switch is closed and the fifth bulb is removed
a) Current flows through whole circuit.
b) Current flow stops at the second bulb because circuit is interrupted.
c) Current flows through rest of circuit, bypassing fifth bulb.
Calculate the missing quantities for the circuit below.
A30. V1 = 7.5 V
R1 = 5.0 
R2 = 3.0 
Calculate the missing quantities for the circuit below.
A31. V1 = 40 V
R1 = 2.0 
V2 = 40 V