Sparking an Atttraction

Today at the elementary we built electromagnets.  First I asked each table to prove that they were ready by getting a light bulb to light up given a battery and a few wires.  From their time with teacher Lorie they should have learned that electricity has to travel in a circuit, and most of them were able to do that fairly quickly.  To move on to the electromagnet, each table had to pass a test: if they switch the wires on the light bulb, will it still light up?  Many of them said no quite confidently, but regardless of what they predicted I made them do the experiment.  I then explained how the bulb (a small incandescent bulb for a flashlight or nightlight...the simplest, cheapest type of light bulb) works.  It heats up when electric current passes through, and gets so hot it glows.  This mechanism is so simple that it doesn't even matter which direction the current passes through.  Fancier light bulbs (LEDs) might be more persnickety.

For the electromagnet I told each table to wind a wire tightly many times around a 10d nail.  (Unlike the website linked to in the previous sentence, I didn't bother with switches; we just held things together with electrical tape and/or fingers.) As they finished, some of them asked me what to do next, and others just started trying things.  I gave only vague hints to those who asked, such as "Figure out how to pass electricity through it."  The trick is to make a complete circuit, just as with the light bulb, but they really had to think and experiment (and receive some more hints) before getting it.  This just shows how hard it is to transfer knowledge learned in one context to another context.

After the first session, I figured out that the best way to respond when asked what to do with the wire-wrapped nail is to ask them to check if it's magnetic yet.  This serves two purposes (1) makes them develop a procedure for checking if it's magnetic, which I wanted them to do at some point anyway (picking up a paper clip is the best test I know of); and (2) see that you need flowing current to make the electromagnet work.  After some current flows, the nail tends to get permanently magnetized, making it less obvious later on that current is necessary.  Therefore it's best to demonstrate early on that there is no magnetism.  Also, if you reuse materials from earlier experiments you might well get materials that have accidentally been permanently magnetized.  You'll want to check for this before handing materials out.

For tables which had time left after proving to me that their electromagnet functioned, I gave additional challenges.  Some I challenged to make 2 light bulbs light up.  To others I gave permanent magnets and asked them to figure out how to magnetize a nail without electricity.

All in all this was a pretty good 45-minute activity, with no lecture by me (although it is good to emphasize at some point that this demonstrates that there is a connection between electricity and magnetism).  The one downside was that any circuit more complicated than a single bulb or nail was impossible to keep together with tape and fingers, and one of the younger kids got very frustrated even with a single bulb.  If I were to do more circuit experiments, I would prep by soldering wires on to the light bulb and battery terminals.  This had crossed by mind beforehand, but I thought that this might be giving too much away; I wanted them to figure out the relevant parts of the light bulb.  So in the future I might have one set of bare bulbs for beginners, and one set of bulbs with leads for those who want to make more complicated circuits which don't fall apart.  (Those who don't like soldering might consider using sockets and wires with crimp connections, etc.)