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ADAPTERS
How many adapters can you find in your home? Adapters are small black boxes that plug directly into wall outlets. If you put your ear next to one while it's plugged in, you will hear the "60 cycle hum" sound made by all line transformers. As you probably have found out, adapters burn out every now and then, especially if you leave them plugged in all the time.
WITH ADULT ASSISTANCE: Find one that is no good anymore and take it apart. (Don't plug it in!) Inside you'll see some small electronic parts that change the AC outlet voltage into DC. The largest and heaviest part is the transformer. Peel off some of the plastic coating and you'll see coils of copper wire. There may be a spot that looks burnt. This is where wires short-circuited and ruined the adapter.
Cut one of the wires, then unwind some. Use a knife to scrape the wire at one end and look at it closely. You will see that the wires are coated with a thin layer of insulation that keeps the electricity from short-circuiting to the other windings in the coil. This is called bell wire. Save some bell wire to make your own electromagnets, motors, and generators.