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Physical Science

Content Benchmark P.8.B.2
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 Physical Science Matter Force and Motion P.8.B.1 P.8.B.2 P.8.B.3 Energy Content Areas Nature of Science (NOS) Life Science Earth Science Physical Science

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.

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.

magnetic field can create an electric current.">
Figure 2. A magnet rotates between two conductors and induces an electric current.

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.

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)

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.

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 step-up 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

1st Item Specification: Understand the relationship between electric currents and magnetic forces.

Depth Of Knowledge Level 1

1. For a magnet to induce an electrical current in a stationary coil of wire, the magnetic field  must be
1. static.
2. changing.
3. strong.
4. weak.
1. Which of the following will be surrounded by a magnetic field?
1. A wire that is conducting an electrical current.
2. An aluminum rod that has been touched by a magnet.
3. Two copper wires held close together.
4. A pot being heated on an electric stove.
1. Which of the following will increase the strength of the magnetic field in an electromagnet?
1. Decreasing the current in the wire that surrounds the iron core.
2. Removing the iron core from the center of the electromagnet.
3. Decreasing the number of loops of wire around the iron core.
4. Increasing the number of loops of wire around the iron core.
1. The diagram below is of a solenoid, which is a type of electromagnet used to make on-off switches. Use this diagram to answer the next question.

What part of the electromagnet is identified by the letter A in the diagram above?

1. The magnetic field.
2. The electrical current.
3. The core of the electromagnet.
4. The source of electrical current.

Depth Of Knowledge Level 2

1. Which of the following is NOT true about the relationship between electricity and magnetism?
1. Generators use magnets to induce an electrical current.
2. Motors use electrical currents to create a magnetic field.
3. A magnetic field can be used to induce an electrical current.
4. All magnets are surrounded by an electrical field.
1. Use the diagram below to answer the next question.

Electricity">
From: http://www.school-for-champions.com/science/electromagnetic_devices.htm

Moving the magnet back and forth through the coil of wire will cause which of the following to occur?

1. Electrical current will flow through the magnet.
2. Electrical current will flow through the wire.
3. The magnet will become stronger.
4. The magnet will lose its magnetic field.
1. Sean and Shanika conducted an investigation to compare the number of turns of wire around the iron nail in an electromagnet, to the number of paper clips the electromagnet could pick up. Their data appears on the graph below

How does decreasing the number of turns in the coil of wire affect the strength of the magnetic field of the electromagnet?

1. The magnetic field does not change.
2. The magnetic field becomes stronger.
3. The magnetic field becomes weaker.
4. The magnetic field disappears.
1. Which of the following devices work because an electric current is used to create a magnetic field?
1. A generator and a windmill.
2. A generator and an electric motor.
3. A bar magnet and a battery.
4. An electric fan and a vacuum cleaner.

Constructed Responses P.8.B.2

1. Use the following diagram to answer the question below.

When the switch is closed, an electromagnet will be formed.

1. Circle the electromagnet in the picture?
2. Explain what an electromagnet is.
3. Why must the switch be closed in order for the electromagnet to work.
1. Use following picture of an electromagnet made from an iron nail wrapped with coils of wire to answer the following question.

The more turns of wire there are around the soft core of iron, the more paper clips the electromagnet will pick up. Observe the data on the table and answer the question below.

 Number of turns in the coil of wire of an electromagnet. Number of paper clips picked up by the electromagnet. 5 2 10 4 15 8 20 10
1. Construct a line graph comparing the number of turns of wire on the electromagnet to the number of paper clips it can pick up.
2. Explain why the electromagnet picks up more nails as the number of coils increases.

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

Answers to Sample Test Questions

1. B, DOK level 1
2. A, DOK level 1
3. D, DOK level 1
4. A, DOK level 1
5. D, DOK level 2
6. B, DOK level 2
7. C, DOK level 2
8. D, DOK level 2

Constructed Response 3-point Answers and Score Rubrics:

Constructed Response #1

 3 points Response addresses all parts of the question clearly and correctly. An electromagnet is formed when electricity creates a magnetic field around a metal like iron that can be magnetized. Closing the switch allows the electricity to flow. When the electricity flows the electromagnet will work. Student answers must include three the following: (a) The wire-wrapped nail is the electromagnet. (b) An electromagnet is a magnet created by an electrical field. (c) Electricity will not flow if the switch is not closed. (d) Electricity is needed to make the nail magnetic/create the magnetic field. 2 points Response addresses all parts of the question. Student answers include only two of the following: The wire-wrapped nail is the electromagnet. An electromagnet is a magnet created by an electrical field. Electricity will not flow if the switch is not closed. Electricity is needed to make the nail magnetic/create the magnetic field. 1 point Response does not address all parts of the question. Student answers include only one of the following: The wire-wrapped nail is the electromagnet. An electromagnet is a magnet created by an electrical field. Electricity will not flow if the switch is not closed. Electricity is needed to make the nail magnetic/create the magnetic field. 0 point Response is totally incorrect or no response provided. Electricity or magnetism listed without explanation. Not answered or off-task.

Constructed Response #2

 3 points Response addresses all parts of the question clearly and correctly. The electromagnet picks up more paper clips when there are more turns of wire around the nail because the magnetic field becomes stronger. Student answers must include the following. (a) A line showing the directly proportional relationship between the number of turns of wire and the number of paper clips picked up. (The graph must be a line, not bars). (b) Data points on the line representing the number of turns of wire and the number of paper clips picked up. (Bars acceptable if they are accurately placed). (c) Explanation that more turns of wire will cause the magnetic field (magnetism) to be stronger. (d) Correct labels for both x-axis and y-axis. 2 points Response addresses all parts of the question and includes only minor errors. 1 point Response does not address all parts of the question. 0 points Response is totally incorrect or no response provided.

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

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.