Ch. 3; Lesson 3.3/3.4
T.O.C:
Magnetism Can
Produce Current
Magnets Generate
an Electric Current
• DNW- When a magnet moves inside a coiled wire w/in a circuit, an
electric current is generated in the wire. However:
• It is easier to generate an electric current by moving a wire inside a
magnetic field.
• Whether u move the magnet or the wire; the effect is the same:
– Current is generated as long as the wire crosses the magnetic
field lines.
Generating an Electric Current
• Generator(w.w) device that converts the energy of motion (kinetic energy), into
electric energy.
• If you manually turn the shaft of a motor that contains a magnet, you can produce
electric current.
• B/c it does not need to be plugged in, a generator can be used wherever/whenever it
is needed.
How It Works
1. As the handle turns, it rotates a series of gears. The gears turn the shaft of the
generator.
2. The rotation of the shaft causes coils of wire to rotate w/in a magnetic field.
3. As the coils of the wire cross the magnetic field line, electric current is generated.
The current recharges the device.
Direct & Alternating Currents
• *Remember* electrons flow from one end of a battery/generator, thru the
circuit, & back to battery/generator.
• Electrons that flow in one direction produce 1 of 2 types of current
1.
2.
Direct Current (DC)(w.w) electric charge that flows in one direction only. Produced by
batteries & DC generators.
Alternating Current (AC)(w.w) flow of electric charge that reverses direction at regular
intervals. (it goes forward & backward) Current in homes/schools use this.
• These 2 currents are produced by different generators.
• Most devices can use both types of current but Some appliances can use
only direct current
• A car generator a.k.a the alternator keeps all electrical devices working
including battery
•
•
•
•
Magnets are used to
Control Voltage
Transformer(w.w) device that increases or decreases voltage.
Transformers use magnetism to control the amount of voltage.
Transformers are used in distribution of current.
Transformers consist of 2 coils of wire wrapped around an iron ring. (Illustration).
– 1st coil is tighter/more coils. Alternating current from voltage source enters coil & creates
a magnetic field so the iron ring becomes an electromagnet.
– 2nd coil is inside a changing magnetic field. Current is generated in the 2nd coil which is
looser & has less coils. This changes the amount of voltage allowed to pass thru which
protects homes/devices
*A transformer w/ equal coils is a step-up transformer. A transformer like
above is a step-down transformer.
DEMO
3.3 Review Q’s 11 pts
1. What is necessary for a magnetic field to produce an electric
current? (2 pts)
2. How do electric generators convert kinetic energy (energy of
motion) into electrical energy? (2 pts)
3. What are 2 differences in which direct current and alternating
current are generated? (2 pts)
4. What is a car generator called? What is its function? (3 pts)
5. On the inside, why does a step-down transformer have
less/looser coils on the 2nd coil than the 1st coil? (2 pts)
Ch. 3; Lesson 3.4
T.O.C:
Generators Supply
Electrical Energy
Generators Provide Most
of the World’s Electrical Energy
• What generates electricity to your
home?
– The tremendous energy produced by
falling water provides the turning motion
for large generators at power plants.
• For Ex: The Hoover Dam power plant
supplies energy to more than a million
ppl!
• Other sources of energy found at power
plants include: steam from burning fossil
fuels (coal), nuclear reactions, wind, solar
heating, & ocean tides.
Continued…
• How does the power plant convert the
energy of motion into electrical energy?
You ask…
• Great Question!!!  Large generators in
the plant hold powerful
electromagnets surrounded by massive
coils of copper wire. And
1. As the water falls from the reservoir, its
kinetic energy increases & it flows very fast.
The falling stream of water turns a turbine
(fan-like device) which is connected to the
generators shaft.
Think of this on a much larger
scale for a generator in a power
plant…
Nuclear Power Plant
•
Electric Power Can Be
In order to provide
electrical energy to homes
Measured
& factories , power companies need to know
the rate at which energy is needed.
• Power companies need to know how much
power is used & where. This is how they know
how much to charge for your electric bill.
Watts & Kilowatts
• Watt(w.w) unit of measurement for power.
– Measures the rate at which energy is used by an
electrical appliance.
– Formula for finding power in watts ~ Electric power
(P) = Voltage (V) x Current (I)
– Ex: 40 W v. 100 W. Brighter bulb converts energy at a
higher rate than a lower power bulb
• Kilowatt(w.w) unit of power equal to 1,000
Sample Problems
• Sample: Watts & Kilowatts- Electric power (P) = Voltage (V) x Current (I)
• If a device uses 50 volts and 40 amps (current), how many watts does the
device use?
– Answer- 2,000W; or 2 kW
• If a device uses 1,500 watts of power and 30 amps (current), how much
voltage does the device use?
– Answer- 50 volts
• If a device uses 300 watts of power and 10 volts of power, how much current
(amps) does the device use?
– Answer- 30 amps
• Sample: Kilowatt-hour- Energy used (E) = Power (P) x time (t) (in full
hours)
• How much energy is used if a 3,000 W (3 kW) clothes dryer is used for 4
hours?
– Answer- 12 kWh
• How much energy is used to dry clothes in a 3 kW dryer for 30 minutes?
– Answer- 1.5 kWh
3.4 Review Q’s 12 pts
1.
2.
3.
4.
5.
How do power plants generate electrical
energy from kinetic energy? (2 pts)
Explain what watts measure. (2 pts)
How is energy use determined? (2 pts)
All of the appliances in the computer lab
are in use for 6 hours every day &
together use 3.3 kW. How much energy
has been used in 1 day? SHOW YOUR
WORK (3 pts)
A hair dryer uses 400 watts of power