Magnets, Electromagnets & Fields of Force

5150 South Blackstone
Chicago IL 60615
(312) 535-1407

Objectives:

Students will perform activities that enhance their understanding of the
following:
*Magnets exist only as dipoles.
*A field of force exists around any magnet.
*Only items containing nickel or iron are attracted to magnets.
*Temporary magnetism can be induced by placing iron or nickel into a
magnetic field.
*The movement of current through a wire is accompanied by a magnetic
field.

Materials needed:

Enough good, strong pairs of magnets so that each person in class has a
pair.
A paper/plastic plate and a ZipLok bag large enough to enclose the plate
for each member of the class.
A quantity of powdered iron/iron filling.
Enough wire (16 to 22 gauge enameled) so that each member of the class has
Enough (steel) nails (16 penny sinkers or larger) so that each member of
the class has one and a similar sized non-ferrous nail or rod: use aluminum,
brass, plastic,copper, wood (even a pencil).
Enough dry cells (11/2 volt C, D, or "ignition") so that each member of the
class has one.
Sandpaper, for removing insulating coating from wire.
A large quantity of very small nails (brads).
Optional Power supply with output 12volt@>4amps, approximately 10m wire
coiled into loop of about 10cm, neodynium magnets (approx. 2cm2 by 1/4cm
thick), compasses (of the type used in orienteering)

Strategy:

Dipoles & Fields 1. Encourage students to test the repulsion/attraction of magnets. How does the magnet's orientation effect this phenomenon? How can we label the ends of our magnet? 2. Line up magnets in such a way, or on such a device that they will pivot easily. What does moving one do to others? Do magnets have to touch each other to interact? 3. Will magnets stand on thin edge more easily if they are aligned to Earth's poles? Why? 4. Give students plate/bag with iron powder inside. Touch magnet to outside of bag. What happens? Does the way that magnet contacts bag/plate effect the iron fillings? 5. Hold plate parallel to ground, with iron powder in a compact heap. Hold magnet against plate. Slowly tilt plate so powder runs toward spot above magnet in a sheet-like flow. What happens? What sort of pattern results? Draw it! 6. Repeat the above step holding the magnet against the plate in a different way-- if it was perpendicular before try parallel or vice verse. Try to make a map of the three dimensional field by adding these two-dimensional sets of information. Electromagnets & Magnetic Metals 1. Begin by having students wind (coil) about half of their allotted wire around their steel nail. Expose the bare copper by sanding off coating. Contact the two free ends to the two terminals of the dry cell. How many nails can you pick up with this electromagnet? 2. Coil the rest of the wire onto the nail. Does the winding direction matter? Test the number of nails picked up. 3. How does the wire feel when it is hooked-up to the dry cell? Does using the electromagnet deplete the battery rapidly or slowly? Why? How might this be improved on? 4. Hold the electromagnet near the "ZipLok Field Mapper". Map the field! 5. Slip the coil off the nail. Try to do this while the electromagnet is connected. What happens to the strength of the magnetic field? Verify your results by using the "Field Mapper". 6. Slide a different material into the coil. What happens? Repeat with metals and non-metals. Does it matter if the metal is a poor conductor or good conductor? How can you explain this? Does it matter if the metal is hollow or solid? Optional Really cool demonstration from the Oersted Experiment. Place a really strong magnet in or near the 10cm loop of 10m of wire. Turn on the power supply for a very short period of time (doing otherwise might short
your power supply or burn up the wire). You've built a very crude solenoid.
Try reversing the polarity. Try changing the position of the magnet. Try
mapping the field. See what happens with a compass, or a whole bunch of
compasses arranged around the coil (or inside it). What does this tell you
about the operation of an electromagnet? What does this suggest about the role
of the nail in an electromagnet?

Performance Assessment:

The best proof of learning is in the production of something useful. The
goal is to build the strongest electromagnet you can. First plan out what
materials you need and how you will connect/build your electromagnet. Creative
solutions are appreciated, but consider how each element of your design
contributes to the goal. This is called design efficiency, use it! In order to
minimize the variables leading to success, a regulated 11/2 volt power supply
should be substituted for dry cells. Similarly a pan of nails that is not
susceptible to tampering is preferred over paperclips, which students may link
into chains. Other means to ensure fairness should be discussed before the
competition, as students are badly discouraged when they perceive someone
cheated to win. If the rules are "anything goes" be prepared to require
students to supply their own materials and set some spending limit (verified by
receipts and/or catalog prices) that cannot be exceeded. Efforts to instill
fairness in competition pay off with students working harder on the thinking and
designing and caring less about the legality or the "the winner".

Conclusions:

The idea that the flow of an electric current is accompanied by a magnetic
field revolutionized scientific understanding and has made possible most of
modern life. The generation of electricity would not be possible without
knowledge of this. Similarly all electric motors operate by taking advantage of
this. The fame Ampere holds is directly traceable to Oersted's disclosure of
his work at the September 1820 meeting of the Acadmie Royale des Sciences in
Paris. The cooperative nature of science is clearly illustrated, as is the
relative recency of the discovery.

Evaluation:

Students should answer the questions presented in the strategies. If
their understanding is correct they should receive credit for this. If their
understanding is lacking they should engage in more activities and this
additional work should be acknowledged. Students who do not work and/or do not
understand will harm themselves and the advancement of humanity.

References:

R.S. Kirby et al, Engineering in History. New York, McGraw-Hill.
R.A.R. Tricker, Early Electrodynamics: The First Law of Circulation. Pergamon Press. William Gilbert, de Magnete. London, Royal Academy of Science.
J. Czerwiec, Early Understanding of The Natural Philosophers.
Unpublished