1. What do you think? `
An iron nail is attracted to an iron magnet but not to another nail. Two magnets can attract each other.
Is either end of the nail attracted to either end of the magnet?
Is either end of one magnet attracted to either end of the other magnet? Explain.
Both are made of iron, but the magnet behaves differently. Why?
How does the nail change when near the magnet so that it is attracted?
When asking students to express their ideas, you might try one of the following methods.
(1) You could ask them to write their answers in their notebook and then discuss them.
(2) You could ask them to first write their ideas and then share them with a small group of 3 or 4 students. At that time you can have each group present their consensus idea. This can be facilitated with the use of whiteboards for the groups.
The most important aspect of eliciting students’ ideas is the acceptance of all ideas as valid. Do not correct or judge them. You might want to ask questions to help clarify their answers. You do not want to discourage students from thinking about these questions and just waiting for the correct answer from the teacher. Thank them for sharing their ideas. Misconceptions are common and can be dealt with if they are first expressed in writing and orally.
Students likely will know the answers to the first two questions but the last two questions ask for an understanding of WHY this occurs. Encourage them to think about how the particles inside the nail might behave differently than those in the magnet.

2. Properties of Magnets
Magnets attract metals classified as ferromagnetic.
Iron, nickel, cobalt
Magnets have two poles, north and south.
Like poles repel each other.
Opposite poles attract each other.
When free to rotate, the north pole points toward the north.

3. Magnetic Domains
In ferromagnetic materials, groups of atoms form magnetic domains within the material.
In a paper clip or nail, the domains are randomly arranged.
In a magnet, the domains are more aligned.
Students could investigate the model using electron spin to help understand why some materials are ferromagnetic.
The domains each have their own magnetic fields. When they are somewhat aligned, the magnetic fields add to give a net magnetic field.

4. Magnetic Domains What would happen to the domains?
They would better align.
How would the paper clip be different afterward?
It would behave as a magnet.
Would it remain magnetized?
The domains would gradually become more randomly oriented.
Suppose you rubbed a paper clip repeatedly in one direction with the north pole of a magnet.
Magnetic materials are classified as hard and soft.
With soft magnets, it is easier to align the domains, but they do not hold the alignment as long.

5. Magnetic Fields What object is used to detect a gravitational field?
Any mass - when released it falls in the direction of the field
What object was used to detect an electric field?
A positively charged test particle - when released it moves in the direction of the field
What object would be used to detect a magnetic field?
A compass - the north pole points in the direction of the magnetic field
Students may have seen iron filings used. Iron filings or paper clips also detect magnetic field,s but they do not tell you which way it is going (because they do not have a north and south pole). They simply align in the field, which could be going either direction.

6. Magnetic Fields Compass needles show the direction of the field.
Out of the north and into the south
The distance between field lines indicates the strength of the field.
Stronger near the poles
The field exists within the magnet as well.
The PhET website may be useful at this time.
Choose “simulations,” then choose “Electricity, Magnets and Circuits,” then choose “Faraday’s Electromagnetic Lab.”
At this time, it would be useful to show them the “Bar Magnet” option.
You can show a compass and the field. There is also a meter to measure the strength of the field at various points.

7. Earth’s Magnetic Field
The north pole of a magnet points toward the geographic north pole or Earth’s south magnetic pole.
Opposites attract
The magnetic poles move around.
The magnetic and geographic poles are about 1500 km apart.

8. Earth’s Magnetic Field
Which way would a compass needle point in the U.S.?
Toward the north and slightly downward into Earth
Field lines go into Earth as seen in the diagram; they are not parallel to the surface.
Earth’s poles have reversed many times in the past, as evidenced by core samples showing differing magnetic field directions.

9. What do you think?
Electromagnets are used every day to operate doorbells and to lift heavy objects in scrap yards.
Why is the prefix electro- used to describe these magnets?
Is electricity involved in their operation or do they create electricity?
Would such a magnet require the use of direct current or alternating current?
Why?
When asking students to express their ideas, you might try one of the following methods.
(1) You could ask them to write their answers in their notebook and then discuss them.
(2) You could ask them to first write their ideas and then share them with a small group of 3 or 4 students. At that time you can have each group present their consensus idea. This can be facilitated with the use of whiteboards for the groups.
The most important aspect of eliciting students’ ideas is the acceptance of all ideas as valid. Do not correct or judge them. You might want to ask questions to help clarify their answers. You do not want to discourage students from thinking about these questions and just waiting for the correct answer from the teacher. Thank them for sharing their ideas. Misconceptions are common and can be dealt with if they are first expressed in writing and orally.
Students may be familiar with electromagnets but unclear about their operation. Help them clarify their ideas about how electromagnets operate.

10. Magnetism from Electricity
A compass needle held near a current carrying wire will be deflected.
Electric current must produce a magnetic field.
Discovered by Hans Christian Oersted
Many compasses placed around a vertical current carrying wire align in a circle around the wire.

11. Right-Hand Rule
To find the direction of the magnetic field (B) produced by a current (I):
Point your right thumb in the direction of the current
Curl your fingers and they will show the direction of the circular field around the wire.
Remind students that current (I) is opposite the flow of electrons.

12. Magnetic Fields
C B A
Use the right hand rule to decide what direction the magnetic field would be at points A, B, and C.
Since magnetic fields are vectors, how would the net field appear in the center of the loop?
The fingers of the right hand should always curl around the wire and upward through the middle. This creates a magnetic field that comes out of the top of the loop and into the bottom of the loop. This is demonstrated in the Visual Concepts clip on the next slide.

13. Magnetic Field of a Current Loop
Click below to watch the Visual Concept.
Visual Concept

14. Magnetic Field Around a Current Loop
Magnets and loops of wire have magnetic fields that are similar.
Solenoids are coils of wire similar to the single loop.
More loops strengthens the field
Placing an iron rod in the center strengthens the field as well
Called an electromagnet
For solenoids, all loops must go in the same direction to make the B fields additive.
An iron core will become magnetized by the field and thus adds its own B field to that of the solenoid.
Do the quick lab in this section of the Student Edition, and hold a compass near the end of the coil with the nail and without the nail to demonstrate the enhancing effect of the iron core.
The PhET website may be useful at this time.
Choose “Simulations,” then choose “Electricity, Magnets and Circuits,” then choose “Faraday’s Electromagnetic Lab.”
At this time, it would be useful to show students the “Electromagnet” option.
You can show a compass and the field. You can reverse the electron flow (note that it is the opposite the direction of current) by adjusting the potential difference. You can also change the number of loops in the solenoid. There is an AC option as well.
Ask students what will happen with each case before running the simulation.

15. Charged Particles in a Magnetic Field
The right-hand rule for the force on a moving charged particle
Thumb in the direction a positive particle is moving
Fingers in the direction of the magnetic field
The force will be in the direction of your palm
For negative particles, the force is out the back of your hand.

16. Force on a Charge Moving in a Magnetic Field
Click below to watch the Visual Concept.
Visual Concept

17. Magnetic Force as Centripetal Force
Use the right-hand rule to determine the direction of the force.
Which direction would the force be when the charge is at the top? the left side? the bottom?
Always directed toward the center
Because of this magnetic force, the charge moves in a circle.
The force is centripetal.
Charged particles entering Earth’s atmosphere get trapped into circular motion by the magnetic field and spiral toward the poles. This phenomenon causes the northern and southern lights.

18. Parallel Current-Carrying Wires
Current carrying wires create a magnetic field which interacts with the moving electrons in the nearby wire.
Currents in the same direction produce attraction.
Currents in opposite directions cause the wires to repel.
Use the-right hand rule to verify the direction of the force for each of the four wires shown.
Remind students that the direction for I is that of positive charge. The electrons are moving in the opposite direction.
In order to verify the direction of the force, students will need to imagine the B field extending over to the other wire. For example, in the top diagram, the B field from the left wire at the right wire would be into the page. Therefore, since the positive charge is moving upward, the force would be to the left.

19. Applications - Cathode Ray Tube
Televisions and computer monitors use CRTs.
A magnetic field deflects a beam of electrons back and forth across the screen to create an image.
Have students look up more information about how a television produces an image (a CRT television, not LCD or plasma).
“HowStuffWorks.com” is a web site with good information.

20. Applications - Speakers
The forces on electrons as they move back and forth in the coil of wire cause the coil to vibrate.
The coil is attached to the paper cone, so sound waves are produced by the vibration.