Page #5: Winding the Field Magnets

When each field magnet (or any of the electromagnets, for that matter) is wound, it is best for students to work in pairs, with one doing the actual winding and the other holding the spool on a spare 125mm spike and dispensing the wire as it is needed. This helps to keep the wire from getting kinked. Few pupils, however, will manage to wind their electromagnets entirely without kinks. If the kinks are not too “tight”, the wire should be very gently straightened. If, on the other hand the kinks are severe, it is better not to try straightening them because the copper conductor is much more likely to break inside the vinyl insulation. Electromagnets wound with kinked wire won't be as pretty as would otherwise be the case, but they will work just fine... as long as the copper isn't broken.

Some older students, especially those with larger hands and/or better-developed fine motor control (no pun intended), may prefer to wind their field magnets without the help of a classmate. The photograph below shows one way that this can be done. The spool of wire is allowed to rotate in one hand, while the wire is fed out between the thumb and index finger of the same hand. Mr. de Demeter has found that this method works best for him.

Be sure to wind the field magnets according to the directions indicated in the diagram accompanying the downloadable instructions accessible from page 11. Keep in mind that, for the sake of simplicity, this diagram shows only one layer of windings. However, the wire shown coming straight down from the top of each spike actually represents a second layer of windings placed on top of the first. As indicated in the printed instructions, about 250mm of wire should be left free at each end of each field magnet winding. These free ends can be temporarily held in place with the thumb tacks.

Once the two field magnets are finished, they should be “energized” and tested. If the battery connections and brushes are properly configured, the top of one field magnet will be a NORTH pole, while the top of the other will be a SOUTH pole. This can be checked with a compass needle. If they both have the same polarity, simply switch the brush and battery connections for one (and only one) of the two field magnets.

Correct orientation of the windings may also be confirmed with the so-called “right-hand rule” for the polarity of electromagnets. If you place your right hand on an electromagnet so that the fingers are aligned with the windings and point in the direction of positive current flow, then your thumb will point towards the north pole.

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