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Chapter 7
Section 3
Circuits
How many electrical devices can you see in this room?
Circuits have:
1) source of voltage difference (battery or outlet)
2) device that uses the energy (light)
3) conductors (wires) form a closed path to device
Series Circuit
Example: A string of Christmas lights, when one light burns out,
no lights will work. Why? Because that burned out bulb
breaks the circuit to all the bulbs.
Each bulb along the
path shares the
voltage, so the bulbs
may appear dim.
Parallel Circuits
Series circuits aren't a good way to wire a
house. If you turned off one light, then all
the lights would go out.
Parallel circuits contain two or more
branches
Disadvantage: Even when you turn a light
off, current continues to flow through the
system.
This is why you shouldn't stick a fork in an
electric socket!
A switch can break a circuit
And turn a device on or off
Would this switch
still work?
Identify the type of circuit:
______________________
______________________
Symbols for writing a circuit
What is a fuse?
Fuses contain a tiny
piece of metal that
melts if the current
gets too high - this
breaks the circuit.
Too many appliances
on in one room can
overload the circuit
and blow a fuse.
Where does electricity come from?
Most electricity comes from converting heat energy into
electrical energy - burning fossil fuels such as coal and
natural gas.
Some electricity is generated from dams, and nuclear reactors
How do dams generate electricity?
As water flows
through the dam it
spins turbines,
which will create
electricity.
These are referred to
as:
HYDROELECTRIC
DAMS
Electricity by magnets
• Magnets have a magnetic field. This field can
manipulate the flow of electrons which
means it can produce electricity. By moving
or turning a magnet you can force the flow of
electrons.
Cost of Electricity
1) Most companies charge by the
amount of energy used
2) This is measured in kilowatt
hours (kWh)
3) Each light bulb in your house
costs money to leave on!
4) Meters outside your house
measure how much energy is
usedCheck out:
http://www.energyeducation.tx.gov/
What is the difference between
alternating current and direct current?
Check out
http://www.pbs.org/wgbh/amex/edison/s
feature/acdc.htmlhttp://www.pbs.org/
wgbh/amex/edison/sfeature/acdc.ht
ml
AC = alternating current
DC = direct current
Direct Current is found in
simple circuits like a battery
powered flashlight.
Alternating Current
The direction of current flowing in
a circuit is constantly being
reversed back and forth. This is
done with any type of AC
current/voltage source.
AC power is used in homes and
business. It's cheaper and
easier to make devices for AC
power, and you can easily
increase and decrease the
current.
1. What happens when an object has an excess number of
electrons?
2. Name something that is a conductor:
3. What unit is electric current measured in?
4. What unit is electric energy measured in (think power bill)?
5. The force that causes electrons to flow is the ____________
difference.
6. Is the image showing a
parallel or series circuit?
7. Where does the
electricity come from that
powers your house?
8. What causes a fuse to
be blown?
9. _________ Law can be
used to calculate voltage.
10. Resistance is the
tendency for ____________ to
oppose the flow
of ____________.