Magnets, Electromagnets, and Motors

Lynne Nolan                    Naperville Central High School
                               440 W. Aurora Ave.
                               Naperville IL 60540
                               708-420-6417

Objectives:

     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 
        electric motor.

Materials Needed:
   
Materials needed are listed with the strategy to which they apply.

Strategy:

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 
           demos below)
        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.

D. Motors...
     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 
motor.
     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.

Performance Assessment:

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?
Rubric:
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.

Multicultural Emphasis:
 
      Dans la langue de votre choix, vous pouvez enseigner cette lesson.  Suivez 
le planning precedent.  Donnez-moi un coup de telphone si vous avez besoin de 
la vocabulaire.