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Electric Circuits
Chapter 22 Section 3
Electric Circuits
• If you connect a conductor (wire)
between + and – terminals of
battery, electrons flow in circuit
• Amount of current determined by
voltage of battery and resistance of
conductor
Voltage & Resistance
• As voltage increases, electric current
in a circuit increases ( V , I )
• As resistance increases, electric
current in a circuit decreases
(, I ↓)
• Remember: Ohm’s Law
V = IR
voltage = current x resistance
Circuits
• Control movement of electric
current by providing paths for
electrons to flow
• Must provide an unbroken path for
current to flow
• Two kinds of basic circuits:
– Series circuit
– Parallel circuit
Series Circuit
• Circuit that has only one path for
electric current to follow
• Path broken—current will no longer
flow and all devices on circuit stop
working
• In series circuit, all electrical devices
are connected along same current
path
– Current is same through each device
• Each new device added to the circuit
decreases the current
– Each device has electrical resistance
– Total resistance to flow of electrons
increases as each additional device is
added
– By Ohm’s law, if voltage is constant,
I  as 
Series Circuit
Broken Series Circuit
Parallel Circuits
• Circuit that has more than one path
for electric current to follow
• Current branches so that electrons
flow through each of the paths
• If one path broken, electrons
continue to flow through the other
paths
• Resistance in each branch can be
different depending on the devices
– The lower the resistance, the more
current through the branch
– Current in each branch of parallel
circuit can be different
Parallel Circuit
Broken Parallel Circuit
Protecting Circuits
• As current through the circuit
increases, wires carrying current
heat up
• To keep wire from becoming too hot
and causing fire, houses & buildings
have circuit breakers that limit the
amount of current in the
wiring
• When current becomes too large—a
switch opens in the circuit breaker
and stops the current
• Once the cause of overload is
removed, circuit can be used again
by resetting the breaker
Cost of Electric Energy
• Power—the rate at which energy is
used
– Amount of energy that is used per
second
• Amount of electric energy used
depends on power of device and
amount of time used
• Electric companies sell electric
energy in units of kilowatt-hours,
kWh
– Equal to using 1 kW of power
continuously for 1 hr
• Charges customers for number of
kWh used every month
– Measured by an electric meter
(attached to home)
Electric Safety
• 1997—electric shocks killed an
estimated 490 people in United States
• Prevention is the key
– Never use appliances with frayed cords
– Unplug appliances before working on them
– Avoid water when using plugged-in
appliances
– Never touch power lines with anything
Electric Shock
• Your body is like a piece of insulated
wire
– Fluids inside body are good conductors
• Current can enter your body when
you become part of an electric
circuit
• The effect of electric current on the
body depends on the amount of
current that flows into the body.