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Electromagnetism-Oersted's Needle (Mark Pichaj)

...in which our hero, Danish science teacher Hans Christian Oersted, performs a lecture demonstration, and in perhaps the ultimate discrepant event in the history of science, makes an earth-shaking, civilization-making discovery: magnetism and electricity are indeed closely (albeit, perpendicularly) related!  In fact, they are both aspects of the same force, but it will be more than half a century before the two actions-at-a-distance are unified by James Clerk Maxwell in his electromagnetic theory.  Suffice it to say, Oersted's discovery kicked off a mad search for the fundamental relationship between electricity and magnetism, a search which involved men with names like Ampere, Henry, Faraday, Maxwell, a search which led to the discovery of electromagnetic induction (1831) and electromagnetic radiation (1864)—and the founding of the modern world of technology.


Our Hero:

Hans Christian Oersted

(1777-1851)

(Wikimedia Commons)


Author(s)

Mark Pichaj . . . and Hans Christian Oersted!  (See above.)


Principles Illustrated

Electromagnetism...which led to electromagnetic induction!  (Enough said, yes?)


A "Galvanometer"—Son of Oersted's Needle!

D'Arsonval galvanometer movement.
(From Wikimedia Commons)


Standards

Grade Four, Physical Science, 1. b.-f.:  electricity, magnetism & electromagnets

Grades Nine-Twelve, Physics, 5. f.-g.:  electrical currents a source of magnetic fields


Procedure

            (1)  Place a compass with a transparent case on an overhead projector so that the motion of the needle is clearly visible to the class.  Bring a magnet near the needle to show how the two magnets influence each other.
            (2)  Using some sort of ammeter, demonstrate to the class that a Genecon hand-powered generator produces an electrical current when cranked.
            (3)  Connect a short (10-15 cm) piece of copper wire (either insulated or uninsulated) across the two alligator clip leads of the Genecon generator.  (It should be long enough to allow it to be held across the compass on the overhead projector, while still leaving a clear view of the motion of the needle.)
            (4)  Hold the wire across the compass in such a way so that it is exactly perpendicular to the compass needle.  Ask students to predict what will happen to the compass needle when someone (perhaps a student volunteer) begins to crank the Genecon.  Have her crank the Genecon, and observe the behavior of the needle.
            (5)  Now hold the wire across the compass so that it is roughly parallel to the needle.  Ask students to predict what will happen this time.  Have the student crank the Genecon, and observe the results.
            (6)  Finally, have the student assistant reverse the direction in which she is cranking the Genecon.  Ask students to predict what will happen, and then observe.  
            (7)  You have just perfomed the same demonstration that H. C. Oersted did back in 1819, and shown that electricity and magnetism are two related forces, and that their relationship is a perpendicular one.


Questioning Script

Prior knowledge & experience:

Like gravity, electricity and magnetism were known from antiquity to be two distinct types of mysterious "action at a distance" forces.  There was no reason to expect that they would be related in any way, as one seemed to be dependent on friction between dissimilar materials, and the other on lodestones and iron.  And if they were by some chance able to influence each other, surely a current-carrying wire would drag a compass needle to point in the same direction as the current flow.  Surely.  Most forces act like simple pushes and pulls through direct contact.  But these forces are more like gravity: a "spooky" action at a distance.

Root question:

Are electricity and magnetism related in some way?  Could one force influence the other?  How could we show this relationship?  What would we have to do to get one to influence the other?  Specifically: In what direction must electricity flow to force the deflection of a compass needle?

Target response:

•  When studying the behavior of the natural world to support or falsify a hypothesis, rigorously investigate obvious relationships between two phenomena, but be also be diligent and creative in the investigation of less apparent relationships.

•  Natural phenomena (like certain forces) might be only one aspect of a more fundamental phenomenon, and can be reduced or unified in such a way so as to produce a more complete explanation of the natural world.

Common Misconceptions:

•  If the forces of magnetism and electricity were in some way related, that influence would show itself (1) in a parallel relationship (as we are usually accustomed to observing forces interact), not in a perpendicular relationship, and (2) in force vectors that were straight lines, not some sort of Aristotelian circular vector!

•  Furthermore, although the more advanced physics student is familiar with vector addition (for instance, the perpendicularity of the acceleration and velocity vectors of an object in a ballistic trajectory), electricity and magnetism are related on a far more fundamental, ontological level.  The forces of electricity and magnetism can be unified into one force, namely, electromagnetism.


Photographs and Videos

(1)  Photos of an Oersted's Needle demo from the University of Montana archive of physics demos.

(2)  An image of an Oersted's Needle from 1828 from the Science & Society Picture Library.

(3)  A vintage Oersted Magnetic Needle (steel & mahogany); click on the image for a video.

(4)  A replica of H.C.O.'s original demonstration compass!

(5)  An interactive Oersted's Compass from the Univ. of Florida's National High Magnetic Field lab.

(6)  A Flash animation of Oersted's Experiment from Edumedia.

(7)  The "Oersted Experiment" conducted with a common flashlight battery and a compass.

The Oersted Experiment



(8)  A "how to" video from phyisfun.

Magnetic Effect of Currents



References

(1)  "Hans Christian Oersted" in Wikipedia:                      http://en.wikipedia.org/wiki/Hans_Christian_Ørsted

(2)  "Episodes in Romantic Science" from the University of Florida:  http://www.clas.ufl.edu/users/fgregory/oersted.htm

(3)  "Oersted's Magnetic Needle" from the Museu de Fisica at the Universidade de Combra:  http://museu.fis.uc.pt/140ing.htm

(4)  "Hans Christian Oersted" from the Institute of Chemistry at the Hebrew Univ. of Jerusalem: http://chem.ch.huji.ac.il/history/oersted.htm

(5)  "Oersted, electric current & magnetism" at Practical Physics:    http://www.practicalphysics.org/go/Resources_13.html

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