Magnetism
Page 1
MAGNETISM
Permanent Magnets
Magnetism ....... ............ ............ ............ .......... 2
Magnets--What Are They Good For? ..... .......... 3
Magnetic Attraction ...... ............ ............ .......... 4
Magnetic Fields ............ ............ ............ .......... 5
Magnetic Poles. ............ ............ ............ .......... 6
The Earth is a Magnet... ............ ............ .......... 7
Magnetic Mystery #1 .... ............ ............ .......... 8
Magnetic Mystery #2 .... ............ ............ .......... 9
Make Your Own Compass......... ............ ........ 10
Make Your Own Magnets.......... ............ ........ 11
Demagnetizing a Magnet ........... ............ ........ 12
Magnetic Strength......... ............ ............ ........ 13
Magnetic Levitation ...... ............ ............ ........ 14
Magnetic Shielding....... ............ ............ ........ 15
Mystery Needles ........... ............ ............ ........ 16
Magnetic Separation ..... ............ ............ ........ 17
Magnetic Games ........... ............ ............ ........ 18
Magnetic Fields in 3 Dimension ............ ........ 19
Bibliography
Appendix: Figures, Explanations
List of Materials Needed
Magnetism
Page 2
Magnetism
Magnetism is a fascinating, mysterious, and
easily accessible topic for elementary school
children to explore. Magnetism is also one of the
most difficult, least-understood subjects in modern physics. But don't let that concern you.
There are lots of things we can do with magnetism that all of us can understand.
In our exploration of magnetism we will
learn what makes a magnet and investigate
magnets of different sizes, shapes, and strengths.
We will learn a basic vocabulary of magnetism.
We will learn how to make our own permanent
magnets, and with our homemade magnets we
will make compasses, space ships, boats, and
other toys. We will also learn that electricity and
magnetism are related, and how to make simple
electromagnets.
This set of activities is organized into two
areas: permanent magnets and electromagnets.
Each area is subdivided into different activities.
We will not have time to do all the activities, but
by the end this session you should be able to do
any of the activities we have skipped.
This magnetism section contains a series of
one page descriptions of a number of activities.
The description is enough to get you started, but
it doesn't contain all the answers. We will discover many of the questions and answers as we
explore. (In science, discovering what the questions are is as important as finding the answers.)
The activity sheets fulfill several purposes. They
help you get started with the activity, and they
should be used to record your observations as
you proceed. We have set aside some space for
you to record any pitfalls you may notice. That
way you can save yourself and others future
grief.
There is a section on each activity sheet
titled "Classroom Use." Only you know best
how you can use (or not use) the material we
present. One of the goals of this workshop is to
develop lesson plans based on our activities. The
activity sheets plus the filled-in section on
"Classroom Use" make up the core of a lesson
plan. We would also like to know what grade
level you think the activity is appropriate for.
All of these activities will help you satisfy
the new Show-Me Standards. Each activity
includes a list of the "performance" standards
(also called Goals) and "knowledge" standards
which the activity will help you teach.
There is also a section on each activity sheet
marked "Comments." We want to know what
you think of these activities. If an activity is the
greatest thing since peanut butter, let us know. If
an activity is confusing, dumb, or ridiculous, let
us know also, and don't spare any harsh words.
At the end of each lesson, or of each day, please
copy your comments to the feedback forms we
will provide, so we have access to them after you
leave.
Books on activity-based science are available
at most public libraries and book stores. Jane
Haskell of Rolla Middle School has ordered
many of them for her school library, and may be
able to direct you to sources of books. We also
have a number of books and science kits available at this workshop. You may check them out
and take them home while you are here. In
reading these books, you may find that there are
many activities, but only a few unique ideas,
which most of the books contain. The books
differ mainly in how they dress up the ideas for
presentation. Following the magnet activity
sheets is a list of books we have used in preparing this material. A few of the activities borrowed heavily from particular books. In those
cases, the books are cited on the individual
activity sheets.
Magnetism
Page 3
Magnets--What Are They Good For?
Materials Needed: Your thinking cap.
Concepts: Applications of magnets.
Activity: Group discussion. Make a list of places where magnets are used. How many can you
come up with? If you're stuck, try looking around.
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Magnetism
Page 4
Magnetic Attraction
Materials Needed: Magnet, your imagination.
Concepts: Magnets attract some objects but not others.
Activity: Magnets will attract or be attracted to certain materials, and not to others. Before you
start this activity, fill in the blanks (to the best of your current knowledge):
Magnets are attracted to
.
Magnets are not attracted to
.
Use your magnets to make a list of those things which attract and those which do not attract. A
suggested format with examples is given below. Use the back of this sheet if necessary.
Object
Composition of Object
Attracts?
soft drink bottle
glass
no
car key
metal
yes
house key
metal
no
Comments
looks like brass
After you complete this exercise, review your answers to the fill-in-the-blank questions above.
Were you right?
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
Classroom Use: How would you use this activity in your classroom?
Your Comments:
Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Further Investigation: Just what is a magnet made of?
Magnetism
Page 5
Magnetic Fields
Materials Needed: Magnets, iron filings, one or more compasses, paper plates.
Concepts: Magnets are surrounded by a "force field."
Activity: The action of a magnet is rather mysterious, isn't it? We have seen that magnets can
attract objects even from a distance. Let's learn about this "force field" around a magnet.
• Put one or more magnets underneath a paper plate. Sprinkle a small amount of iron
filings on a paper plate. Describe what you see. Try it with a bar magnet with N and S poles.
Could you use the pattern in the iron filings to draw a picture of a magnetic field?
• With a magnet in place underneath the plate, hold a compass just above the iron filings.
Which way does the compass needle point? Slowly move the compass around, just above the
iron filings. What does the compass needle do? Do you see any correlation between the
direction the compass needle points and the pattern of the iron filings?
• You can also sprinkle your iron filings on stiff paper (such as index cards) or glass or
plastic sheets.
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
Keep iron filings out of the eyes. Do not dip magnets directly into the filings (children are guaranteed to do this).
Classroom Use: How would you use this activity in your classroom?
Comments: Please write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Magnetism
Page 6
Magnetic Poles
Materials Needed: Magnets.
Concepts: Magnets have north and south poles.
Activity: You may already know that all magnets have north and south poles. You probably
noticed the "N" and "S" markings on the bar magnets we used in the Magnetic Fields activity.
You also observed the presence of these poles during the iron filings experiments. Let's
experiment with the idea of magnetic poles a little more. Take the different magnets you have
and hold them close together in a variety of orientations. Describe what happens. Do magnetic
poles always have to be at the ends of a magnet? Can you find the poles of all of your magnets?
• Experiment with some magnetized nails/pins/straightened out paper clips. Can you find
the poles?
• Take two magnetized nails or pins and lay them on the table parallel and close together,
but with opposite poles next to each other. Slowly move one towards the other. What does the
other one do? Now do the same but with like poles next to each other.
• Is it possible to make a magnet with only a north pole? With only a south pole? Could
you devise an experiment to test your answers?
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Further Investigation: Try to make a magnet with only a north or south pole. Use a compass
to find out what happens.
Magnetism
Page 7
The Earth is a Magnet
Materials Needed: Styrofoam ball, colored toothpicks
Concepts: The earth acts like a large, weak magnet.
Activity:
• Stick a blue toothpick in your ball to represent the earth's geographic north pole. Stick a
red toothpick in your ball to represent the earth's geographic south pole.
• Check: does everybody's earth look OK so far?
• Stick a yellow toothpick in your ball to represent the earth's magnetic north pole. Stick
a green toothpick in your ball to represent the earth's magnetic south pole.
• Compare "earths." Whose earth best represents reality?
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1,
4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication
Arts 1.
Further Investigation: Get a globe depicting the earth. Explain why the globe is oriented as
it is. Have the earth's magnetic and geographic poles always been aligned? Discuss the
consequences of your answer. Use foam balls and toothpicks to model the earth in your
classroom.
Magnetism
Page 8
Magnetic Mystery #1
Materials Needed: Compass.
Concepts: How a compass works.
Activity:
1. Without using your compass, try to decide which direction is north. Note that
direction; but don't use your compass to figure it out.
2. Put your compass on the table in front of you.
3. Compasses are generally made with a colored end which points north, and a noncolored, or maybe silver end, which points south. Look at your compass, observe which
direction is north, and stand by your compass with your right arm pointing north. No
cheating. Don't point some direction just because your neighbor points that way--they
might be wrong!
4. Do you see anything interesting?
5. Have I made any statements which might be false?
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Magnetism
Page 9
Make Your Own Compass
Materials Needed: Nails, pins, paper clips, water containers, water, corks, styrofoam cups,
aluminum foil, scissors, detergent. (Not all of these are needed.)
Concepts: Needle shaped permanent magnets are used to make compasses.
Activity: Make a compass based on one of the three following designs. (1) Cut off thin slices
of corks; (2) cut off the bottom quarter inch or so of a styrofoam cup; (3) fold a small piece of
aluminum foil in the shape of a boat. Magnetize your nails/needles/paper clips. By now you
should know how to magnetize them so that they have both north and south poles. Place them on
the cups/corks/boats in a container of water. If they tend to float to the side of the container, add
a little detergent to the water (do you know what the detergent does?).
• What do your floating magnets do? Do you notice anything unusual about the direction
in which they point? Use a bar magnet to help answer the last question.
• Do you know of any other designs for a homemade compass?
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
If you are teaching young children, you should probably avoid using pins, knives, or razor blades.
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Further Investigation: Exactly how does one use a compass?
Magnetism
Page 10
Magnetic Mystery #2
Materials Needed: Bar magnet, compass.
Concepts: North and south poles.
Activity: The following questions will lead you through this activity. Answer them one at a
time. Consider your answers carefully; there are no tricks, but correct logic is necessary.
Complete steps 1 through 6 first. We will discuss the results together before we proceed further.
1. Fill in the blanks:
magnetic poles attract and
magnetic poles repel.
2. True or false: a compass is just a magnetized needle floating on a low-friction
bearing. Circle one: true false.
3. The earth's geographic and magnetic poles nearly coincide. Therefore the needle of
the compass that points north (i.e., is attracted to a north magnetic pole) is actually the
needle's
magnetic pole.
colored end of your compass needle points north. Therefore, that end of
4. The
the compass needle is actually the needle's
magnetic pole.
5. A bar magnet has N and S poles at each end. The end of the bar magnet labeled "N" is
the bar magnet's
magnetic pole.
6. Experiment with your bar magnet and compass. Observe how the compass needle
"follows" the bar magnet. Caution: if your bar magnet is powerful enough, it is possible
to demagnetize and then remagnetize the compass needle so that its magnetic poles are
switched. Before you continue, double-check that the answer you gave to (4) is still
colored end of your compass needle points north. Therefore, that end
correct: the
of the compass needle is actually the needle's
magnetic pole.
7. After you complete (6), fill in the blanks: the
is attracted to the end of the bar magnet labeled
colored end of the compass needle
("N" or "S", fill in one).
8. Is there anything interesting about your results? (There should be.) Can you explain
your results? If you can't, do one of the following:
•Get your local high school physics teacher to explain.
•Get a local college or university physics professor to explain.
•Carefully repeat the experiment, have faith in your logic, and believe your
results. There is a logical explanation.
•Call or write me. I'll be glad to explain.
•Take the UMR "Activity-Based Physical Science Class for Elementary and
Middle Schools" and learn the answer there.
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Magnetism
Page 11
Make Your Own Magnets
Materials Needed: Magnets, nails, needles, pins, paper clips.
Concepts: Most materials which are attracted to magnets can also be made into magnets.
Activity: Take a nail out of the box. Does it pick up paper clips? (See figure 1.) If it does, find
one that doesn't. Now hold it against a magnet, and while maintaining contact with the magnet,
see if the nail picks up paper clips (figure 2). What has happened? What have you done to the
nail? Remove the nail from the magnet and see if the nail still holds up paper clips (figure 3).
Repeat the above with pins instead of nails and note any differences.
• Take a nail or pin which doesn't attract paper clips. Stroke it a few times across your
magnet. Now what can you do with the nail?
Fig. 1
Fig. 2
Fig. 3
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
If you are teaching young children, you should probably avoid using pins.
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Further Investigation: Many science textbooks say that in order to magnetize a nail you must
stroke it in one direction only across a magnet. Is this true? What kinds of materials can you
magnetize? Can you magnetize a pencil?
Magnetism
Page 12
Demagnetizing a Magnet
Materials Needed: Magnets, nails, pins, steel strip, iron filings.
Concepts: Materials which are easy to magnetize are often easy to demagnetize.
Activity: Take one of the nails you magnetized in the Make Your Own Magnets activity. Is it
still magnetized? Do you know how to demagnetize it? How about the paper clips? Can you
demagnetize the needles?
• Take a strip of transformer steel and hold it against a permanent magnet. Is the strip a
magnet? Remove it from the magnet. Does it remain magnetized? Can you explain your
results?
• Take a paper clip, hold it in contact with a permanent magnet, and pick up one or two
paper clips with it (pick them up with the end not in contact with the permanent magnet, see fig.
1). Carefully remove the permanent magnet and the paper clips should remain attracted (fig. 2).
Bring the opposite pole of the permanent magnet close to the first paper clip (fig. 3) and explain
what happens. You can also try this with the nails and paper clips, as in the previous activity.
• Can you magnetize a jar of iron filings? Do the filings attract paper clips? What
happens when you shake the jar?
• Now that you are an expert demagnetizer, can you demagnetize the needle?
Fig. 1
Fig. 2
Fig. 3
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
If you are teaching young children, you should probably avoid using pins. The steel strips also have sharp edges.
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Further Investigation: Explain how magnets become magnetized/demagnetized.
Magnetism
Page 13
Magnetic Strength
Materials Needed: Magnets, nails, paper clips.
Concepts: Magnetic strength depends on magnet composition, size, shape, etc.
Activity: Take one of your magnets. How many paper clips or nails can it pick up? Does the
number of paper clips picked up depend on where they are attached to the magnet?
• If you stack two magnets together, will the pair pick up twice as many paper clips as an
individual magnet? Make a prediction and then test your prediction:
Prediction:
Result:
.
.
Would 1000 times as many magnets pick up 1000 times as many paper clips?
• Take a different magnet, predict how many paper clips it will pick up, and test your
prediction.
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Magnetism
Page 14
Magnetic Levitation
Materials Needed: Magnet, paper clips, pins, nails, tape, thread.
Concepts: Magnetic force can overcome gravitational force.
Activity: This works best with pins or straightened-out paper clips (cut the paper clip in half for
best results). Tie 5 or 6 inches of thread to a paper clip, pin, or small nail. Tape the loose end of
the thread to the table and bring a magnet close to (but not in contact with) the untied end of the
paper clip/pin. What happens? Slowly move magnet around the paper clip/pin, and describe
what happens.
• Can you make the pin "dance"? Can you find the poles of the magnet this way?
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
If you are teaching young children, you should probably avoid using pins.
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Magnetism
Page 15
Magnetic Shielding
Materials Needed: Magnets, paper clips, nails, paper, sheet steel.
Concepts: Magnetic fields can pass through some objects but not others.
Activity: Use your levitating paper clips/nails/pins. Devise some
kind of holder for the magnets so that they levitate the pins without
you having to hold the magnets; that way you have both hands free for
the activity.
• Predict what will happen if you put a piece of paper (or
several) between your magnet and levitating pin. Now try it. What
does happen?
• Put a variety of other materials between your magnet and levitating pin. What happens?
• How many sheets of paper can you put in between and still maintain levitation? How
many strips of steel?
• Explain your observations. What materials do magnetic fields penetrate? What
materials act as magnetic "shields"?
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Magnetism
Page 16
Mystery Needles
Materials Needed: Two needles.
Concepts: You may have trouble telling what is a magnet and what is simply being attracted to
a magnet.
Activity: Get two identical unmagnetized needles. Magnetize one of them. Mix them up
thoroughly so you can't remember which is which. If you are tempted to "cheat" get a friend to
mix them up. Is there a way to tell which one is the magnet without using any object other that
the two needles themselves?
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Magnetism
Page 17
Magnetic Separation
Materials Needed: Magnet, salt, iron filings, paper.
Concepts: An application for magnets.
Activity: Mix together the salt and iron filings on a sheet of paper. By now you should be able
to figure out how to separate the iron filings from the salt. Note the "Special Care" section
below.
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
Don't dip the magnets directly in the iron filings; hold them under the paper plate. Naturally, children are guaranteed
to dip the magnets into the iron filings.
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Suggested Grade Level:
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Further Investigation: What else can you do with this idea?
Magnetism
Page 18
Magnetic Games
Materials Needed: See descriptions of games.
Concepts: Here are some brief games and activities with magnets.
Space Ship Docking Station. Magnetize some nails or paper clips and tie a few inches of
thread to one end. Make cardboard space ships and insert the nails. Tape the "space ships" to the
table around a large magnet supported on a glass or paper cup. You have made a space ship docking
station. How many space ships can you dock?
Magnetic Pick-Up Sticks. Clip a toothpick to a paper clip. Make several. Put all the
clips/sticks in a loose pile. Who can pick up the most "sticks" one at a time without moving any of
the others? You lose your turn if you move more than one stick.
Treasure Hunt. Hide a prize. Have a treasure hunt. Use compass directions to guide hunters to
the treasure.
Floating Magnets. Insert a pencil through the holes of at least three round magnets. Can you
arrange the magnets so that they float?
Fishing Game. Get several long poles (dowel rods, yardsticks, real or toy fishing poles, or even
tree branches will do). Tie one end of a length of thread to a magnet, the other end to the "pole."
Attach "fish" to paper clips and go fishing. The fish could be: prizes, pieces of paper with
questions to answer or stunts to do, etc.
Another Way to Make a Magnet. Take a long steel rod. Any long (a foot or two) iron or steel
rod or bolt will do. Use the compass to see if it is magnetized. Because it is steel, it should attract
the compass needle. Can you tell if the rod is actually magnetized? Now hold the rod in a northsouth direction, incline it at about a 20E angle to the north, and strike it a number of times with the
hammer. Is the rod magnetized now? Explain why we did the above procedure. Can you guess
how to demagnetize the rod?
"Cutting" a Magnetic Field. Levitate a paper clip or similar object, as you did in the Magnetic
Levitation activity. "Cut" the magnetic field with scissors. What really happened?
Magnetic Faces. Draw a head on a paper plate. You can leave off the hair. Put a small amount
of iron filings in the paper plate, cover the top with plastic wrap, and tape the plastic wrap securely
all the way around. Use a magnet to move the iron filings around and put "hair" (or whatever
decorations you want) on the face. Can you think of a way to preserve your masterpiece?
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
Further References:
(1) Safe and Simple Electrical Experiments.
(2) Teaching the Fun of Physics.
Magnetism
Page 19
Magnetic Fields in Three Dimensions
Materials Needed: Magnets, small jar, salad oil or baby oil, iron filings.
Concepts: Magnetic fields exist in three dimensions.
Activity: We have already done activities where we investigated magnetic fields in two
dimensions; for example, iron filings on a flat piece of paper. Now take a small jar, fill it with
salad or mineral oil or something of a similar consistency, and add enough iron filings to just cover
the bottom. Seal the jar, shake it up, and use some of your magnets to investigate magnetic fields
in three dimensions. Another variation is to put a small magnet inside the jar along with the
filings.
Special Care: Please write down any pitfalls you notice. Do any parts of this activity require
special care?
Messy!
Classroom Use: How would you use this activity in your classroom?
Comments: Write down your comments on this activity.
Show-Me Standards:
Goals: 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 3-1, 3-2, 3-3, 3-5, 3-8, 4-1, 4-6.
Knowledge Standards: Math 1,6; Science 1,2,6,7; Communication Arts 1.
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BIBLIOGRAPHY
Graf, Rudolf F. Safe and Simple Electrical Experiments. New York: Dover Publications, 1973.
Herbert, Don, and Ruchlis, Hy. Mr. Wizard's 400 Experiments in Science. Prism Publications,
1968.
Herbert, Don, and McKie, Roy. Mr. Wizard's Supermarket Science. New York: Random
House, 1980.
McGill, Ormond. Science Magic. New York: Prentice Hall, 1986.
Tolman, Marvin N., and Morton, James O. Physical Science Activities for Grades 2-8. West
Nyack, NY: Parker Publishing Co., 1986.
VanCleave, Janice Pratt. Teaching the Fun of Physics. New York: Prentice Hall, 1985.
Walpole, Brenda. 175 Science Experiments to Amuse and Amaze Your Friends. New York:
Random House, 1988.
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Bar Magnet
Field From a Current Loop
Solenoid
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Magnets--What Are They Good For?
Here are some places magnets are used: anything that has an electric motor, door latches,
can opener lid holders, junkyards, automobile dealers (stick-on temporary license plates),
recycling (separate iron from other metals), televisions, radios (speakers), tape recorders, vcr's,
computer disks and disk drives. There are many many others.
Magnetic Attraction
Only three elements are magnetic at room temperature: iron, cobalt, and nickel. There
are thousands of compounds, containing more than one element, which are magnetic at room
temperature, but it is a pretty safe bet that they contain iron, cobalt, or nickel. Lodestone, the
naturally occurring magnet, is an iron oxide. Stainless steels contain iron; some are magnetic and
others are not. Refrigerator magnets are made from barium ferrite (BaFe12O19) or strontium
ferrite. More powerful alnico magnets, often used in speakers, are made of an alloy of
aluminum, nickel, cobalt, and mostly iron. Samarium cobalt (SmCo5) magnets are more
powerful than alnico magnets and are one of the few common magnets not containing iron. The
most powerful magnets are based on Nd2Fe14B, and are made of neodymium, iron, boron, and
typically small amounts of other elements.
If a magnet is attracted to something, it is a pretty safe bet that the "something" contains
iron. Exceptions would be Canadian coins and samarium cobalt magnets. Magnets are not, in
general, attracted to metals. Many metals are nonmagnetic: aluminum, copper, gold, some
stainless steels.
We are talking permanent magnets here, of course. Later we will see that electricity can
be used to create magnetism, in which case you might have a magnet attracted to something not
containing iron.
Magnetic Fields
Magnets are surrounded by invisible "magnetic fields." Magnetic fields are indicated
using lines which, by convention, originate at north poles and end at south poles. A magnet is
strongest where the magnetic field lines are most concentrated, generally at the poles. Iron
filings will line up along magnetic field lines, so you can use iron filings to trace out magnetic
fields.
Magnetic fields exist in three dimensions, although most books show only twodimensional drawings.
Magnetic Poles
Every magnet has a north and a south pole. This is in contrast to electricity, where you
can have isolated positive and negative charges. Every magnet has both kinds of poles; you can
never find a magnet with only a north or only a south pole. Physicists have theorized about the
existence of "magnetic monopoles" (isolated north or south poles) but have never found one
experimentally.
If you cut a magnet in half, each of the halves would be a magnet with a north and a south
pole. If you cut the halves in half, you would still have magnets with both poles. If you were
cutting iron, you would eventually end up with a single iron atom, which would still have a north
and a south pole. If you smashed the iron atom apart, the electrons which came out would be
magnets with north and south poles.
As you probably know, like poles repel and unlike poles attract.
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The Earth is a Magnet
The earth has a magnetic field. It is theorized that nickel in the earth's core gives rise to
this magnetic field. Because we have never been to the core, there are still many unanswered
questions about why the earth is magnetic.
The earth's magnetic poles are located near, but not exactly at, the geographic poles.
Magnetic field lines do not always point exactly north, which is why mariners using compasses
to navigate need charts telling them how their compasses deviate from true north. The earth's
magnetic poles actually move around in a constant, unsteady motion.
Geologists studying rocks containing magnetic materials, such as lodestone, can tell
where the earth's magnetic poles were at times in the past; when a magnetic rock "freezes," it
freezes like a compass needle pointing north/south. The earth's north and south poles have not
always been where they are now. Of course, a small rock or even a boulder has probably moved
over time; scientists use huge lava beds to map past locations of the earth’s magnetic poles.
A compass is just a small magnetic needle suspended on a low-friction bearing. The
needle aligns itself along magnetic field lines, which point from north to south. Because unlike
poles attract, the south magnetic pole of a compass tries to get to the north magnetic pole of the
earth, and therefore points north. The colors on the compass needle have no fundamental
significance. They are just paint so you can tell one end of the needle from the other. Compass
makers usually try to make a colored end point north, but that doesn't have to be the case. Find
out which end of your compass points north before you get lost in the woods. If you don't like
the direction your compass needle points, you can always try using a powerful magnet to
remagnetize the needle in the opposite direction.
Because compasses are attracted to magnetic materials and materials containing iron, they
won't necessarily point north if you hold them near other magnets, other compasses, or anything
containing iron (file cabinets, chairs, stools, tables with iron bolts, automobiles, etc.).
The next xxx paragraphs contain a slightly more detailed discussion of the earth’s
magnetism. We will see when we study electromagnets that magnetic fields are produced by the
motion of electrical charges. The magnetic field of a permanent magnet results from the motion
of electrons in the atoms of the magnet. The origin of the Earth's magnetic field is not
completely understood, but is thought to be primarily caused by electrical currents produced by
the spinning liquid metallic outer core of iron and nickel.
The earth is made of an inner core of solid iron and nickel, surrounded by an outer core of
molten iron and nickel. Outside the outer core is the mantle, a thick, dense, tar-like mixture of
rocks. We live on the crust of the earth, a relatively thin layer of rocks which are less dense than
the mantle and float on the mantle.
There are actually three factors which contribute to the earth’s magnetic field. The
magnetic field is primarily caused by electrical currents flowing in the outer core. Natural and
manmade objects in and on the earth’s crust also contribute a small amount the the earth’s
magnetic field. Electrical currents flowing in upper layers of the earth’s atmosphere also
contribute to the earth’s magnetic field.
The earth’s poles have reversed on average every 200 thousand years. The last time the
poles reversed was about 780 thousand years ago. Are we overdue for a pole reversal? I
wouldn’t lose any sleep over it; when it does happen, it will probably take place over a time
period ranging from months to thousands of years.
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The earth’s geographic pole moves with time in a well-known pattern. The magnetic pole
also moves. The whole story of the earth’s magnetism is very complicated, and scientists are still
working hard to understand it.
Magnetic Mystery #1
See the previous lesson for a discussion of the meaning of the colors on a compass
needle, and the warning that compasses won't work properly if you hold them near anything
containing iron.
I like this experiment because it produces a surprising result, which at first seems wrong,
but has a logical explanation. In science, you get what you get. Don't "fix" the data to get an
expected result. What you got might have been wrong (if that's the case, find out where you went
wrong and re-do the experiment) or your interpretation might have been wrong (if that's the case,
re-think).
Make Your Own Compass
To make a compass, simply magnetize a needle-shaped object and find a way to suspend
it with a minimum of friction. Of course, it helps if your homemade compass is portable, and
remember to keep it away from other magnetic materials if you want it to read accurately.
Magnetic Mystery #2
I like this lesson for the same reasons that I like Mystery #1. It is correct that unlike
magnetic poles attract. If we accept that geographic north is also magnetic north, then the
compass needle's south pole is attracted to the earth's north pole, and points north.
The compass needle's south pole is also attracted to a bar magnet's north pole. If it is
attracted to the pole labeled "S", there are several options:
(1) the experiment may have been flawed (not so in this case)
(2) the bar magnet may have been mislabeled (I have seen a few that were mislabeled!)
(3) the bar magnet manufacturer may have labeled the south-seeking pole with an "S", so
that if you hang the bar magnet by a thread and make it into a compass, the pole labeled
"S" points south, and you, the customer, are happy because the poles appear to be
correctly labeled.
Make Your Own Magnets
You can make a magnet by rubbing a permanent magnet on a nail, needle, paper clip, or
chunk of iron. How long your homemade magnet stays magnetized depends on its shape and
how its atoms are put together. Nails tend to not stay magnetized long, paper clips are better, and
it is hard to find nonmagnetic needles.
The textbooks always say "rub your nail 30 (or 20 or 40 or 60) times always in the same
direction (when the moon is full and the werewolves are howling)." Actually, just touching a
nail to a magnet is enough to magnetize it. Stroking it a few times might help, but don't believe
for a minute that textbook authors personally check out every single statement they make. That
goes for the author of these activity sheets, too.
Demagnetizing a Magnet
A nail is made up of millions of tiny particles, each of which is a little magnet. In most
nails, the particles are randomly aligned, the magnetic fields cancel each other, and the nail as a
whole is nonmagnetic. When you magnetize a nail, you get the magnetic fields of the tiny
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particles to line up more or less in the same direction. Any disturbance which gives the tiny
particles energy is likely to demagnetize the nail.
Magnetic Strength
Magnetic fields of separate magnets add together (if the magnets are aligned properly).
Two identical magnets ought to be more powerful than one alone. A big magnet ought to be
more powerful than a small one of the same material. A way to measure a magnet's power is
how much it picks up; e.g., how many paper clips it picks up. Of course, if you magnetize the
paper clips, you can't tell just how many paper clips are being picked up by the magnet, and how
many are just sticking to each other.
The shape of a magnet also affects its strength. Motor designers go to great lengths
designing the shapes of their magnets. A bar magnet doesn't have the right shape to give you a
lot of lifting power; that's why you often see horseshoe magnets depicted as being stronger than
bar magnets. Of course, the material out of which the magnet is made plays a critical role.
By the way, store your magnets just the way they "want" to be stored, and try not to drop
them, because dropping them may demagnetize them.
Magnetic Levitation
Magnets can lift materials which are attracted to them. If you levitate a pin (or paper clip)
the pin will be most strongly attracted to the magnet's poles.
Magnetic Shielding
Magnetic fields can be interrupted by materials which are attracted to magnets, such as
steel, but pass through objects like your hand and paper as if they weren't there.
Mystery Needles
Hint: remember that magnets are strongest at their poles. Bar magnets can't pick up
anything halfway between their poles.
Magnetic Separation
Magnetic separation is a very useful technology. Try this for kicks: crush some corn
flakes and see if you can pick out the iron which the manufacturer has added for your "benefit."
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Materials Needed
This page contains a list of all items listed as "materials needed" for the permanent magnet
activities.
aluminum foil
bar magnets
colored toothpicks
compasses
corks
detergent
iron filings
magnets
nails
needles
paper
paper clips
paper plates
pins
salad or baby oil
salt
scissors
small jar
steel strips or sheets
styrofoam cups
styrofoam balls
tape
thread
water containers (bowls)
water