F-2 MAGNETS AND MAGNETIC FIELDS
(1) To experimentally plot magnetic field lines from various configurations of magnets.
(2) To qualitatively study some other properties of magnets.
Various bar, horseshoe and ring magnets.
3. ADVANCE PREPARATION:
Read the discussion of magnetic fields and potentials in any good textbook.
4. GENERAL PROCEDURE
Some situations to investigate:
Field maps: Trace all of the field lines fully, all the way to the edges of the paper.
The next section includes analysis questions.
(1) Is it possible to make a magnet with an odd number of poles? If so, why? If not, what would be the relative strengths of the poles?
(2) Is it possible to have a magnet with no poles? Explain. If someone handed you a magnet claimed to have no poles, how could you test that it really is a magnet?
(3) You are given two identical iron bars. One is magnetized, the other is not. By Newton's third law, each exerts a force on the other, and these forces are equal and opposite. Is there any way you could experimentally determine which is magnetized? If not, why not. If so, describe and explain as many different ways as you can discover.
(4) What do electric and magnetic fields have in common? What is different about them?
(5) Older books on elementary physics often used the concept of magnetic pole quantitatively, writing F = (constant)P1P2/R2 for the force two poles exert on each other when they are distance R apart. Unfortunately, poles aren't located at points, but are spread over space. Still, you can check the formula approximately from the maps you made. [When physicists were just beginning to understand magnets, they made very long rod and needle shaped magnets, so the poles were so far apart, the size of the poles was small compared to the dimensions of the magnet, and also so they could study the effect of just one pole of one magnet on just one pole of the other magnet without the other two poles influencing the measurement.]
Text and drawings © 1995, 2004 by Donald E. Simanek.