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Content Benchmark P.8.B.2
Students know electric currents can produce magnetic forces and magnets can cause electric
currents. E/S
Magnetism from Electricity
Great discoveries often occur when an astute observer is focused on achieving entirely different
results. Such was the case in the early nineteenth century when a physicist named Hans Christian
Oersted was conducting a demonstration for his class to show that there is no relationship
between electricity and magnetism. To his surprise quite the opposite occurred. When placed
near a wire carrying electric current, the needle of a compass moved, contrary to previous
demonstrations when it had not. Oersted realized that wire must be surrounded by a magnetic
field, and also, that the orientation of the compass needle to the wire affected whether or not the
needle would move. He experimented further and found that the direction of the magnetic field
depended on the direction of the electric current. Figure 1 shows what Oersted observed during
his demonstration.
Figure 1. A schematic of Oersted’s demonstration
(From http://chem.ch.huji.ac.il/history/oersted.htm)
Other scientists including André-Marie Ampère followed up on Oersted’s findings, providing
further research into the creation of magnetic fields using electrical currents.
To learn more about Oersted’s demonstration and electromagnetism, go to
http://www-spof.gsfc.nasa.gov/Education/whmfield.html.
Without the movement of electric charges, magnetism does not exist. In metals that do not
magnetize, electron pairs spin in opposite directions and their magnetic fields cancel each other
out. When electron pairs spin in the same direction on their axis or when electrons flow through
a conductor, the result is magnetism. Also, certain metals like iron, nickel cobalt, gadolinium,
and dysprosium are considered to be magnetic because their atoms can be aligned in the same
direction. If this pattern becomes disrupted and the atoms are arranged randomly, the metal will
no longer be magnetized.
More information about magnetic fields can be found at
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfie.html.
Electricity from Magnetism
Joseph Henry and Michael Faraday each conducted research to test the hypothesis that
magnetism can be used to produce an electric current. Their research demonstrated the process of
electromagnetic induction in which a current is produced in a changing magnetic field. In order
to create or induce an electric current, the wire or conductor must move through the magnetic
force field. The extensive research establishing that a magnetic field can induce an electric
current and that an electric current can create a magnetic field was soon followed by
technological advances and inventions of devices that operate upon the principle
electromagnetism. Figure 2 demonstrates the basic principle behind inducing an electric current
using magnetism.
Figure 2. A magnet rotates between two conductors and induces an electric current.
(From http://www.physics4kids.com/files/elec_faraday.html)
To access more information about Michael Faraday and electromagnetic induction, go to
http://www.ieee-virtual-museum.org/collection/event.php?id=3456912&lid=1.
Electromagnets
An electromagnet consists of a coil of wire usually wound around an iron core. The core
becomes magnetized when an electric current is sent through the wire coiled around it.
Electromagnets have many essential applications, including picking up metal containing iron in
salvage yards, use in speakers, and in many devices that operate by an on-off switch such as
doorbells. Computer screens work because they receive electron beams from electromagnets.
Magnetic Resonance Imaging (MRI) machines are able to detect cancerous tumors by analyzing
the affect of strong magnetic fields on the human body.
More information about electromagnets can be found at
http://www.howstuffworks.com/electromagnet.htm.
Transformers contain two electromagnets designed to step-up (increase) or step-down (decrease)
voltage in power transmission lines. Lower voltage at the power plant is increased using a step
up transformer for transmission along high-voltage lines, where a greater voltage means lower
energy losses during transmission. A step-down transformer is used to decrease the high voltage
in the transmission lines to lower voltage for use in our homes and businesses. Figure 3 shows a
picture of the use of electromagnetism in a transformer. Notice that the blue coil wire has less
coils than the red wire. If the electricity comes in to the transformer through the red coil a current
will be induced in the blue coil. This would be a step-down transformer because the decrease in
the number of coils. A step-up transformer would work in reverse.
Figure 3. A schematic of a transformer used to increase/decrease voltage in power transmission lines
(From http://library.thinkquest.org/13526/c3c.htm)
Solenoids
A solenoid is a type of electromagnet designed with a coil of wire and a movable iron core called
an armature. Solenoids are commonly used where such actions as latching, locking and
triggering something to start are needed. They are useful as on-off switches in home appliances,
office equipment, automobiles (starter and door latches), and where automatic motion is needed.
Figure 4 shows a picture of a variety of solenoids:
Figure 4. Some pictures of typical solenoids.
(From http://www.solenoids.com/solenoid-tutorial.html)
For an animated view of the structure of a solenoid, visit
http://www.regentsprep.org/Regents/physics/phys03/csolenoid/turns.htm.
Generators
Generators are devices that convert mechanical energy into electrical energy. The mechanical
energy can be supplied by a variety of energy sources including wind, falling water, and steam.
In each case the wind, falling water, or steam causes a turbine to spin within a magnetic field
creating an electric current.
Figure 5. A model demonstrating the principle behind a working generator.
(From http://sol.sci.uop.edu/~jfalward/physics17/chapter9/generator.jpg)
Electric Motors
Electric motors are devices that convert electrical energy into mechanical energy. Observe the
diagram of the direct current motor in Figure 6. When electricity flows through the wire wrapped
around the iron core, an electromagnet is created and the armature spins between the magnetic
poles. The spinning armature can then be connected to a working device to produce motion; for
example, to turn the wheels of a toy car, to run an electric mixer, or to run an electric hair dryer.
Figure 6. The basic structure of a direct current motor.
(From http://www.howstuffworks.com/motor1.htm)
More information about electric motors can be found at
http://www.solarnavigator.net/electric_motors.htm.
Electromagnetic Connections
The concept map below provides a partial visual model of the relationship between magnetism
and electricity. The map can easily be expanded or modified to use with students when
summarizing concepts and vocabulary related to electromagnetism.
Figure 7. Electromagnetism Concept Map.
For a more detailed description of AC (alternating current) and DC (direct current), see
http://www.pcguide.com/ref/power/ext/basicsACDC-c.html.
Electromagnetic Radiation
The relationship between magnetism and electricity also applies to electromagnetic radiation.
The two basic principles that explain the relationship between magnetism and electricity also
explain the behavior of electromagnetic waves: (1) an electric field can be induced by a changing
magnetic field and (2) a magnetic field can be induced by a changing electric field. These waves
include radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays and
gamma rays.
Figure 8. A model of an electromagnetic field, where the
electric field is perpendicular to the magnetic field.
(From http://www.phy6.org/Education/wemwaves.html)
To see an animation of this model visit
http://www.phy6.org/Education/wemwaves.html.
For further information about electromagnetic radiation, see MS TIPS Benchmark P.8.C.1.
Content Benchmark P.8.B.2
Students know electric currents can produce magnetic forces and magnets can cause electric
currents. E/S
Common misconceptions associated with this benchmark
1. Students commonly believe that only magnets produce magnetic fields.
Magnetic fields exist around wires carrying an electric current. Magnetic fields are also
formed around planets like our Earth which is definitely not a large bar magnet. The
following diagrams in Figure 8 show the presence of magnetic fields around a magnet, the
Earth, and wires conducting electric current. In the wire on the left the current is flowing in
the direction of the red arrow and the direction of the magnetic field as shown by the blue
arrow is perpendicular to the direction of current flow. The second two diagrams show the
pattern of the magnetic fields (lines of force) surrounding a wire look and a coil of wire
called a solenoid. Note that the magnetic field lines surrounding the bar magnet extend
outward from the North Pole and inward to the South Pole. Earth’s core is not magnetic as
many people believe. Although the core contains iron it is too hot to be magnetic. However,
electric currents in the hot, molten core are the likely cause of Earth’s magnetic field. The
magnetic north pole of a compass needle will point toward the Earth’s geographic North Pole
which is its magnetic south pole.
Figure 9: Various sources of magnetic fields.
(From: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfie.html)
To learn more about misconceptions associated with electricity and magnetism, go to
http://arxiv.org/ftp/physics/papers/0503/0503132.pdf.
2. Students often incorrectly think of electricity as being produced in a wall socket.
When asked where electricity comes from students often say that it exists in the wires in the
walls of buildings, and that plugging a cord into a wall socket will allow the electricity to be
released. To address this misconception, teachers might provide students with access to
diagrammatic schemes that show the path of electrical current from a power plant, to a stepup transformer for increasing voltage for distance travel, through power lines, to a step-down
transformer for decreasing voltage for home use, to the wiring system of the home, and
ending in an outlet.
For diagrams and explanations of this system visit
www.powerhousekids.com/stellent2/groups/public/documents/pub/phk_eb_ae_001468.hcsp.
3. Many students perceive a magnetic field as a pattern of lines (not a field of force) that
surround a magnet.
The misconception that a magnetic field is a pattern of lines that surround a magnet is
promoted by the way magnetic force fields are traditionally diagrammed. Students perceive a
magnetic field literally as well-defined lines that exist around a magnet. They do not apply
the concept of magnetism as a pulling or pushing force to diagrams of magnetic fields.
Magnetic field lines are representations of the magnetic force field that surrounds a magnet
or a moving charge. In essence, magnetic field lines depict the direction of the magnetic
force at every point along the line. Magnetic field lines do not cross, because that would
show the force field acting in two directions at once. This would not reflect the actual
conditions of the field and the representative magnetic force.
To learn more about the correct scientific understanding of magnetic field lines, go to
http://www.spof.gsfc.nasa.gov/Education/whfldlns.html
4. Electricity is made of electrons.
Because the flow of electrons in a metal is called an electric current, students often
mistakenly generalize this to mean that electricity is made of electrons. In essence, electricity
is involved with any charged particles, including ions. For example, atoms in the chemical
paste in a flashlight cell or the sulfuric acid solution in a car battery have the ability to ionize
and cause an electrical current to flow. However, it is important to note that electricity is still
not the flow of these charge particles through a circuit. Actually, individual charges move at
relatively slow speeds along wires. Electricity is really a transfer of energy as a wave-like
signal that moves very rapidly through conductive material.
For a more detailed description of this misconception and other misconceptions related to
electricity visit
http://www.amasci.com/miscon/elect.html
Content Benchmark P.8.B.2
Students know electric currents can produce magnetic forces and magnets can cause electric
currents. E/S
Sample Test Question
Questions and Answers to follow on a separate document
Content Benchmark P.8.B.2
Students know electric currents can produce magnetic forces and magnets can cause electric
currents. E/S
Answers to Sample Test Question
Questions and Answers to follow on a separate document
Content Benchmark P.8.B.2
Students know electric currents can produce magnetic forces and magnets can cause electric
currents. E/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. Experiments with Various Electromagnets
The MagnetMan site features many useful classroom resources, including activities that let
students explore how electromagnets are used in common objects around the house. This site
even includes the directions for making your own speaker using a Styrofoam cup, a magnet,
and a few other basic materials.
For an in-depth look at electromagnets including a picture file, visit
http://www.coolmagnetman.com/magelect.htm.
2. Building Your Own Electromagnet Lessons
Lesson where students can build their own electromagnets are quite common, but these
particular sites offer meaningful and interesting ways to get students to collect data and make
some important conclusions related to the general science of electromagnetism.
The Jefferson Lab provides directions for making your own electromagnet at their website
http://education.jlab.org/qa/electromagnet.html
The Science Bob website provides some clear instructions for getting students to build and
use an electromagnet, including a video that shows the building process at
http://www.sciencebob.com/experiments/electromagnet.html
In association with the California Energy Commission’s Energy Quest educational website,
there are several science projects related to energy and electricity. One of these projects
involves students building and using an electromagnet. The project is located at
http://www.energyquest.ca.gov/projects/electromagnet.html.
3. Faraday’s Magnetic Field Induction Experiment.
Molecular Expressions: Exploring the World of Optics and Microscopy offers an animated,
interactive diagram and explanation of using a magnetic field to create an electric current.
This activity could be used as a teacher-led demonstration if computers are not available for
the entire class. Please note that the Java applet is required to run this animated simulation.
To view this diagram visit
http://micro.magnet.fsu.edu/electromag/java/faraday2.
4. Electromagnets and Health
Arizona State University’s Department of Electrical Engineering has an informational site on
how electromagnets are used in Magnetic Resonance Imaging (MRI) machines. The site
provides basic information that students can use in researching electromagnets and their
applications. Links at the site also provide information on how to run experiments involving
electromagnetism.
To access their website visit
http://www.eas.asu.edu/~holbert/wise/MRI.htm.
5. Generation of Electricity
There are several good websites that provide information on generation of electricity using
electromagnetic induction. For student research, howestuffworks.com has several resources
that provide information and animations about electrical generation.
To get information about how electricity works, go to
http://www.howstuffworks.com/electricity2.htm.
The Wisconsin Valley Improvement Company provides a colorful, animated, and easy to
interpret model showing how an alternating current generator works. Pictures of actual
generators are also provided.
For further information go to
http://wvic.com/how-gen-works.htm.
Bill Beaty has a step-by-step procedure, including pictures and schematics, on how to build a
simple generator. This would make a great science fair project. The site includes a video of
the generator in action.
For these straight forward directions on how to build a model of a generator go to
http://amasci.com/emotor/electoph.html.
6. Information and Activities about Electric Motors.
There are several good websites that provide information on electric motors. For student
research, howestuffworks.com has several resources that provide information and animations
about electric motors.
For a diagram of an electric motor and an explanation of how one works visit
http://www.howstuffworks.com/motors1.htm.
The Nexus Research group sponsors a website that includes visual directions for making a
simple generator and a simple motor. Also available are related video clips.
Their website can be accessed at
http://nexusresearchgroup.com/fun_science/motors.htm.
Taking a direct current toy motor apart to locate and identify the working parts is an excellent
activity for students. All that is needed is a pair of needle-nose pliers. The motors can be
reassembled after study for reuse. These can be projected onto a wall screen while the
students are taking apart and analyzing their own motors. Students should with a little
guidance, be able to locate and identify the following parts: magnets, armature, brushes, and
the split-ring commutator. When the motor is wired into a circuit with a cell or battery the
motor spins.
For close-up pictures of the outside and inside of a toy motor, go to the website
http://electronics.howstuffworks.com/motor2.htm.