Magnets, Electromagnets, and Motors
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Lynne Nolan Naperville Central High School
440 W. Aurora Ave.
Naperville IL 60540
1. Students will understand the general properties of magnets.
2. Students will understand and make an electromagnet.
3. Students will use electromagnets to do work, and they will make an
Materials needed are listed with the strategy to which they apply.
A. Exploratory (Give as homework the day before the lesson.)
Each student is given two magnets and is told to take them home and explore
the properties of magnets, making as many observations as he/she can. The guide
sheet below might be helpful to direct them.
MAGNETIC PROPERTIES: An Attractive Assignment
1. Do the magnets attract all objects?
2. List 10 objects that are affected by the magnets. Do they have
anything in common?
3. List 10 objects upon which the magnet has no effect? Do these objects
have anything in common?
4. What might affect the ability of a magnet to attract another object?
List as many factors as you can.
5. Is there a limit to the number of things that can be attracted to the
magnet at one time? Test this.
6. Try and locate magnets in your house. Do these magnet show the same
qualities as the ones above?
DON'T FORGET TO BRING YOUR MAGNETS BACK TO CLASS!!!
B. Concept development - "A Magnetic Discussion"
1. List the following on the overhead for students to answer while you
check their homework. MAGNETIC OR NOT (Don't list answers, just items)
REFRIGERATOR DOOR **YES**Students are familiar with this.
SOFA **NO** Students may argue a sleeper sofa has metal, but
most textiles, wood, and foam insulation are not magnetic.
COKE CAN (OR 7UP) **YES**These are made of steel.
PEPSI CAN **NO** These are made of aluminum.
DOLLAR BILL **YES**The ink has a little bit of iron in it, so that
pop and candy machines can tell if its the real thing
and not a photocopy.
CEREAL **NO** HOWEVER, cereals claim to be iron fortified, and
in some cereals, if a magnet is dropped into the box, it can be recovered from
the bottom of the box with iron filings stuck to it. Iron fortified??
2. Go over the above list and include in your discussion student
observations of things that were magnetic in their home. Give as many students
as possible a chance to answer. Lead into the properties of magnets..."Let's
organize all this information."
3. PROPERTIES OF MAGNETS (list these on the board)
1. Attract many, but not all metals. (Iron, nickel = magnetic) (Note
2. Exert a force at a distance. (Magnets don't have to touch an object
to move it. Use the overhead projector to show a magnet pushing
another one along, etc.)
3. Attract or repel another object. Magnets have direction!! Show this
by placing two magnets on the overhead; if they attract initially,
flip one over--now they should repel. (N vs. S) A COMPASS is an
instrument used to detect magnetic fields; the needle is magnetic and
therefore is sensitive to other magnets. LAB 1: Map the forces or
field lines around and/or between two magnets. Trace the magnet(s),
and use the compass to determine the direction of the magnetic field.
4. Can make another object magnetic. (Magnetic Induction)
Show this using a magnet and two iron nails. First, show that the
two nails aren't magnetic. Then magnetize one nail by touching it to
a magnet. Touch the second nail to the first. Observe that they
hang together. (Paper clips work well for this too.) Follow-up
questions could be the following: Is there a limit to how much you
could pick up? Why? What observations support your thinking?
5. PERMANENT vs. TEMPORARY magnet
Ask: What would happen if we took the magnet with two nails hanging
from it and carefully removed the magnet? (Get Hypotheses) Carefully
remove the magnet. The nails retain their magnetism for a short
time. These are TEMPORARY magnets. Permanent magnets will stay
magnetic forever unless something disrupts their chemistry.
THE DOMAIN THEORY
The atomic structure ultimately determines whether an object is
magnetic or not. The Domain theory says that areas of atoms within an object
exhibit magnetism. However if these areas are scattered, then they cancel each
other out and the object is non-magnetic. If they are lined up in a parallel
fashion, all facing the same direction, then the object is magnetic. (This is
easily seen by drawing a picture....unfortunately no graphics allowed here.) To
check for student understanding, ask the following question: Why did the nail
from above become magnetic? Why did it lose its magnetism?
C. Electromagnets: Turning a magnet "on" and "off"
1. Permanent magnet--no "on" and "off", always "on"
2. Induced/Temporary magnet--not always reliable, when will it go off?
3. Electromagnet--Turn current on, and magnetic field is on. Current off
and magnetic field is off.
What is an electromagnet? A moving electron (current) generates a magnetic
field around the wire. Demo: Hook a wire up to a battery; a compass placed
nearby will be deflected. Disconnect battery and compass deflects back to rest.
Why/How is this useful? Many items use this principle: power locks in
cars, electric staplers, furnace relays, for example. The most familiar example
is the junkyard magnet that picks up cars and drops them on top of a stack.
LAB 2: Making a Junkyard Electromagnet
Each group is given some wire, different core materials (nails), a
power supply (batteries), and ten-fifteen minutes to experiment and build an
electromagnet. The group that picks up the most "paperclip cars" wins. Award
magnets as prizes.
If we combine all of our knowledge so far (review the main ideas again),
and go one step further, we can begin to understand and even build an electric
1. Electric motors use current to set up two magnetic fields.
2. These fields are set at right angles to each other.
3. By turning a field on and off (alternating current), we cause little
pushes against the other magnetic field. This allows us to do work;
the flywheel of the motor spins, etc. Demo: a free spinning magnet
at rest can be set in motion by bringing a magnet close to it.
LAB 3: Building a Motor
Using the kit provided, follow the instructions, and build the motor.
(I usually give students two days or a weekend) Kits are from a catalog.
Question: You are stranded on a desert island and have been captured by some
potentially hostile natives. All you have in you pocket are four fairly strong
magnets and some string. You must "wow" the natives in two different ways to
save your life, what will you do?
5 points: The person designed a compass, taught the natives how to use it, left
the island, and navigated back to civilization. Then sold the magnets and began
a new life.
4 points: The person clearly stated two different ideas and convinced you as a
native that they understand magnetism.
3 points: The person has two ideas, but not clearly stated. You aren't
completely convinced or "wow"-ed.
2 points: The person has only stated one idea, or has two ideas that lack
explanation. This answer is poorly stated and incomplete.
0 points: The person threw the magnets at the natives and ran the other way.
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