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