20.3 Electric Circuits
20.3 Electric Circuits
Key Concepts
• What is included in a circuit diagram?
• How do series and parallel circuits differ?
• How do you calculate electrical power?
• What devices make electricity safe to use?
20.3 Electric Circuits
To bring electric
current into a
building, an
electrician installs
wires
_______________
20.3 Electric Circuits
Circuit Diagrams
pathway
An electric circuit is a complete ___________
through which charge can flow.
symbols
Circuit diagrams use ________________
to
represent parts of a circuit, including a
source of electrical energy and devices that
are run by the electrical energy.
20.3 Electric Circuits
Circuit Diagrams
arrows
• ____________
show the
direction of current, from
positive to negative.
Direction of
current
Switch
Energy
source
20.3 Electric Circuits
Circuit Diagrams
• Switches show places where the circuit can be
_____________.
opened
• The circuit diagram also
uses a symbol to
represent
source
the _________
of energy
Direction of
current
Switch
+
• Neg. terminal = _____
Pos. terminal = _____
Energy
source
20.3 Electric Circuits
Series Circuits
If one element stops functioning in a series circuit,
none
__________
of the elements can operate.
If one element stops functioning in a parallel circuit,
still
the rest of the elements _______________
operate.
20.3 Electric Circuits
Series Circuits
one
path
A series circuit has _______
_______
that
each charge can follow.
20.3 Electric Circuits
Parallel Circuits
more
A parallel circuit has ________
than one path
each charge can follow.
20.3 Electric Circuits
Parallel Circuits
parallel
Most circuits in a house are _______________.
Even if one device stops working, the others will
still work.
20.3 Electric Circuits
Power and Energy Calculations
The rate at which electrical energy is converted to
another
________________
form of energy is called
________________
__________.
electric
power
Recall that power is the rate of doing work.
The unit of electric power is the joule per second, or
watt
______________(W).
Power often is measured in thousands of watts, or
____________________
(kW).
kilowatts
20.3 Electric Circuits
Power and Energy Calculations
Electric power can be calculated by
current
voltage
multiplying _____________
by ___________.
power
current
voltage
20.3 Electric Circuits
Power and Energy Calculations
Calculating Electric Power
An electric oven is connected to a 240-volt line,
and it uses 34 amps of current. What is the power
used by the oven?
P = 34 amps x 240 volts = 8,200 watts
power
current
voltage
20.3 Electric Circuits
Power and Energy Calculations
An appliance's power rating lets you know how
much power it uses under ________________
normal
conditions.
Example: An electric stove uses about 6000 watts,
and a microwave oven uses about 1000 watts.
20.3 Electric Circuits
Power and Energy Calculations
You can find the electrical energy used by an
appliance by multiplying ____________
by
power
__________.
time
20.3 Electric Circuits
Power and Energy Calculations
The power rating of a typical clothes dryer is 5.4
kilowatts. If you use the clothes dryer for 2 hours,
what is the energy use?
E = 5.4 kilowatts x 2 hours
= 10.8 kilowatt-hours
20.3 Electric Circuits
Electric power companies usually determine
charges on your electric bill using
Kilowatt-hours
_________________.
A kilowatt-hour equals 3,600,000 joules.
20.3 Electric Circuits
Electrical Safety
Most household circuits usually have an average
voltage of 120 volts.
increases
Each device that is turned on _________________
the current.
If the current exceeds the circuit’s safety limit, the
overheat
wire may _________________.
20.3 Electric Circuits
Electrical Safety
Several methods or devices help make
electrical energy safe to use…
correct
• _______________
wiring
fuses
• ______________
breakers
• circuit ________________
insulation
• _____________________
• _______________
plugs
grounded
20.3 Electric Circuits
Home Safety
melts if
Fuses have an internal wire that ________
a current is too great….prevents current
overload.
“Blowing a fuse”
20.3 Electric Circuits
Home Safety
A circuit breaker is a switch that
_______________
when current in a circuit is too
opens
high…prevents current overload.
The circuit breaker must be reset
before the circuit can be used again.
20.3 Electric Circuits
Personal Safety
insulated
Electrical wiring in a home is _________________
to protect people.
If the insulation is damaged, you may accidentally
touch the bare wire and get a _____________.
shock
Avoid touching electrical devices with
wet
___________
hands, because your hands
conduct current more readily when they are wet.
20.3 Electric Circuits
short
Insulation also prevents ___________
circuits…
when a current finds a short path through a circuit
with ____________
resistance.
less
three
A ____________-prong
plug
can prevent shocks caused by
short circuits.
If a short circuit develops, the current takes an
ground
easier path to the _____________through
the
grounding wire instead of your body!
20.3 Electric Circuits
Electrical Safety
The transfer of excess charge through a
conductor to Earth is called _________________
grounding
Even a small current in your body can cause a
painful shock or
injury.
20.3 Electric Circuits
Assessment Questions
1. A number of light bulbs are connected to an
energy source in a series circuit. What will
happen to the other bulbs if one of the bulbs burns
out?
a.
b.
c.
d.
Nothing will happen.
They will be brighter.
They will be dimmer.
They will turn off.
20.3 Electric Circuits
Assessment Questions
2. A pair of computer speakers are connected to a
12-volt power supply with a current of 1.25 amps
running through them. What is the electric power?
a.
b.
c.
d.
0.8 watt
1.25 watt
12.5 watt
15 watt
20.3 Electric Circuits
Assessment Questions
3. A fuse has a switch that opens to prevent
overheating when the current in a circuit is too
high.
True
False