By Joe Laszlo
Special to The Advertiser
Aloha! Have you ever seen a car being picked up by a crane that has a big, round, disk-like thing at the end of the cable? The disk-like thing was probably an electromagnet.
In one of my recent columns, we made an electromagnet. I’d like to explore that concept a little more.
Easy instructions
Start by getting a box of paper clips, three big nails (16 penny), about 30 feet of wire, a battery, some scrap paper and masking tape. (Note: The wire doesn’t need to be one piece. You can splice shorter pieces together by scraping any insulation off the ends, then twisting them together. Be sure to tape over the splices to prevent any short circuits.)
If you still have your electromagnet from my Dec. 10 column, you can skip ahead to step No. 4 below. If you’re starting fresh, follow these steps.
1. Wrap the scrap paper around the nail two or three times, loosely enough so that you can remove the nail from the coil.
2. Starting at the back of paper coil (the point end of the nail), tape one end of the wire down, leaving about 6 inches free. Now wrap the wire around the nail for 50 turns, being sure to go in only one direction. A turn is once around the nail. Tape the other end down.
3. Scrape the insulation off the ends of the wire. Tape one end of the wire to one pole of a battery. Hold the other end to the other battery pole. Will it pick up some paper clips? How many? The battery I used must have been weak because I didn’t pick up more than three.
4. Next, wrap the second nail with paper and then 100 turns of wire. Be sure that you go in the same direction the entire way. If you get to the head of the nail, continue to wrap the rest of wire on top of the first layer, going back toward the point end of the nail. Tape the free end down.
Attach each wire to a pole of battery the same way you did for the 50-turn magnet. How many paper clips were you able to pick up? It should have been quite a few more than with only 50 turns.
5. Continue with this line of experimentation. Wrap a third nail with some scrap paper and then 200 turns of wire. How many paper clips do you think you can pick up now? Try it. You should have gotten at least two times as many as with 100 turns!
6. Remove the nail from the 50-turn electromagnet. Will the coil alone pick up some paper clips? What about the coil that has 100 turns? What about the coil with 200 turns? Did either alone pick up any paper clips? No? Why not? Think back to what I once said about domains. Domains are the tiny spaces in a magnetic object that have a north pole and a south pole.
Mystery solved
The copper wire has no domains, and so it can’t pick up paper clips by itself. But the coils of wire can have a temporary magnet field. The iron nail inside the coils can become magnetized by the electricity going through the coils. Every turn of the wire around the nail adds that much more force to cause the domains in the iron of the nail to line up north to south, north to south. The electromagnetism of the nail with the most turns of wire is the strongest.
As the magnetism of the nail gets stronger, it naturally has the ability to pick up more paper clips.
Until next time . . . a hui hou!
Write to Dr. Gadget with a question or comment, and we’ll put your name in a drawing to have your picture taken with a gadget. Mail your letter with your name, age, school, name of parent(s) and telephone number, to: Dr. Gadget, c/o The Honolulu Advertiser, P.O. Box 3110, Honolulu, HI 96802, or fax 535-8170. You may e-mail ohana@honoluluadvertiser.com only if you’re 13 or older.
"Dr. Gadget’s Science Machine" is written by Joe Laszlo, a retired science teacher and winner of a Presidential Award for Excellence in Science Teaching. His column alternates in this spot with "Hawai‘i Nature Squad."
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