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Electric Circuits
Chapter 35
A Battery and a Bulb
• In order to light a light bulb, you must
have a complete circuit
• Circuit – any complete path along which
charge can flow
• Electrons flow from the negative part to
the positive part of the battery through
the wire and whatever else is in its path
• The electrons do not “squash up” and
concentrate in certain places; they flow
continuously around a circuit
A Battery and a Bulb
Electric Circuits
• Any path along which electrons can flow is a
circuit
• For a continuous flow of electrons, there must
be a complete circuit with no gaps
• A gap is usually provided by an electric switch
that can be opened or closed to either cut off or
allow electron flow
• In Series – applied to portions of an electric
circuit that are connected in a row so that the
current that goes through one must go through
all of them
• In Parallel – applied to portions of an electric
circuit that are connected at two points and
provide alternative paths for the current
between those two points
Electric Circuits
Series Circuits
•
•
1.
2.
3.
4.
5.
Series Circuit – devices are arranged so that
charge flows through each in turn; if one part
should stop current, it will stop throughout
Series circuits follow 5 important rules:
A break anywhere in the path stops the
electron flow in the entire circuit
The total resistance is equal to the sum of
individual resistances along the current path
The current is equal to the voltage divided by
the total resistance
The voltage drop across each device is
proportional to its resistance
The sum of voltage drops across the
resistance of the individual devices is equal
to the total voltage
Series Circuits
Parallel Circuits
•
•
1.
2.
3.
4.
Parallel Circuit – devices are connected to the
same two points of the circuit, so that any single
device completes the circuit independently of the
others
Parallel circuits follow 4 important rules:
Each device connects the same two points of the
circuit; the voltage is the same across each device
The amount of current in each branch is inversely
proportional to the resistance of the branch
The total current is equal to the sum of the currents
in the branches
As the number of parallel branches is increased,
the overall resistance of the circuit is decreased
Parallel Circuits
Schematic Diagrams
• Schematic Diagram – describes an
electric circuit, using special symbols to
represent different devices in the circuit
• Resistance is shown as a zigzag line
• A battery is represented with a set of
short and long parallel lines (positive =
long and negative = short)
Schematic Diagrams
Combining Resistors in a
Compound Circuit
1 / Req = 1 / R1 + 1 / R2 + 1 / R3 + ...
Combining Resistors in a
Compound Circuit
Req = R1 + R2 + R3 + ...
What’s the Total
Resistance?
10Ω
Parallel Circuits and
Overloading
• Lines carrying an unsafe amount of
current are overloaded
• To prevent overloading, fuses or circuit
breakers are inserted in lines that provide
power
• Excessive current will “blow out” the fuse
or “trip” the circuit breaker, stopping the
current
• A short circuit is often caused by faulty
wire insulation
Parallel Circuits and
Overloading
Homework
• Read Chapter 35 (pg. 548-558)
• Do #16-33 (560-561)
• Do #1-8 in Appendix F (pg. 690)