3. Push the coin into one of the slits so that only a few millimeters protrude. Repeat for the paper clip.
4. Touch your tongue across the coin and the paper clip. You should feel the metal-taste sensation of the electricity that this simple cell generates.
Magnetize a sewing needle, using a AA battery (Chapter 31)
You’ll need:
an old AA battery (don’t use a new battery!)
6 feet (2 m) of insulated wire (You can buy reels of wire from an electronics shop. They come in different colors according to thickness. The green one works well.)
sandpaper or an emery board
2 large darning needles
Scotch tape
a length of thread about 1 foot (30 cm) long
1. Leaving 2 inches (5 cm) of wire free at the end, wrap the wire around the needle, starting 1/4 inch (1/2 cm) from one end. Make sure each coil touches its neighbor. The easiest way to do this is to wind 4 coils at a time—spreading them out along the needle—and then push them together so they touch. Don’t wrap the wire too tightly because you need to remove the needle! When you are 1/4 inch (1/2 cm) from the other end of the needle, continue wrapping over the top of the first layer of wire. This time, instead of making each coil touch its neighbor, just get them as close as you can. Continue until you have 6 or 7 layers of wire. Snip off the wire, leaving 2 inches (5 cm) free at the end.
2. Strip the colored insulation from the two ends, over a length of about 1 inch (2 cm). Do this by rubbing the wire with sandpaper or an emery board. Otherwise, get an adult to scrape the wire with a knife. Hold the two bared wires to the two terminals of the battery. Warning: The coil will get warm, and if the battery is too fresh the coil will get too hot to touch. If that happens, disconnect and allow the coil to cool down before reconnecting.
3. Try picking up a paper clip while the battery is still connected—you have made an electromagnet. When you disconnect one of the wires, the paper clip falls.
4. Using tape, connect the coil to the battery and leave for 1 minute to permanently magnetize the needle. If the coil gets too hot to touch, disconnect one of the wires and allow it to cool before reconnecting. Disconnect the coil from the battery, and then remove the needle from the coil. Try picking up a paper clip—the needle is probably too weakly magnetized to do this.
5. Using a small piece of tape, attach the needle to one end of the thread so it hangs horizontally. Attach the other end to the edge of a table or bookshelf so the needle swings freely. Important: Choose a place with no metal nearby! When the needle stops swinging, make a note of its direction. Gently prod one end of the needle. See if it returns to the same position when it stops swinging (it should be pointing north and south).
6. Make a second magnet by slipping a second needle into the coil and connecting to the battery for 1 minute. Disconnect the battery and remove the needle from the coil. Slowly bring one end of the second magnet toward one end of the first magnet. The suspended magnet will either be attracted or repelled. If you switch ends and try again you’ll get the opposite reaction: like poles repel, opposite poles attract.
Make your own battery and use it to magnetize a needle (Chapter 31)
You’ll actually be making just one cell of a battery. If you made two or more such cells and joined them together, this would be called a battery (of cells).
You’ll need:
an adult helper
25 feet (8 m) of steel strapping (not galvanized)
pliers
2 copper dish scourers
a large bottle of white vinegar (1 gallon or 4 L will be plenty)
1 plastic bucket
2 feet (60 cm) of twin-flex wire (speaker wire from a radio shop works well)
the wire coil from the previous experiment
2 large darning needles (don’t use one you’ve already magnetized!)
some paper towel
a length of thread about 1 foot (30 cm) long
Scotch tape
an old knife
Note: Strapping is a narrow strip of metal, ½–¾ inch wide (15-20 mm) perforated with holes, which is used in plumbing for securing pipes. You can find it in hardware stores.
1. Join the two dish scourers together—side by side—by pulling out loops of copper and twisting them tightly together.
2. Carefully remove the coil of steel strapping from its box, making sure it doesn’t unravel.
3. Separate the two strands of twin-flex wire at either end, so that each free end is about 4 inches (10 cm) long. Ask your helper to strip 1 inch (2 cm) of the plastic insulation from each strand, at each end, using the knife.
4. Connect one of the bared wires to the outer end of the steel coil. Connect its neighbor to one end of the joined scourers.
5. Position the steel coil and copper scourers side by side on the bottom of the bucket. Loosely wrap the scourers in a sheet of paper towel so they don’t touch the coil. Make sure the two connecting wires are separated by paper towel too. Warning: if the copper and steel—or their connecting wires—touch, your battery cell will not work. Drape the rest of the twin-flex wire over the side of the bucket.
6. Carefully slip one of the needles through the center of the wire coil from the previous experiment so that most of it is covered by the coil. Connect each end of the coil to one of the two free ends of the twin-flex wire. Do this by wrapping each one tightly around the bared wire. Important: if you don’t make good contacts between the wires, your needle will not be magnetized.
7. Ask your helper to pour vinegar into the bucket so it covers the top of the copper scourers. Warning: Immediately wash off any splashes—vinegar can damage your clothes. Using a pencil, jiggle the steel coil to remove any air bubbles. Leave the wire coil connected overnight.
8. Disconnect the coil and remove the needle. Suspend the needle by the thread so that it swings freely, as in the previous experiment. Notice the direction in which it settles. Check to see if it returns to the same position after prodding one of the ends.
9. Add about 1 pint (1/2 L) of fresh vinegar and then magnetize a second needle, the same way as before. Keep the coil connected for about 24 hours. Holding the second magnetized needle, use it to attract and then repel, one end of the suspended one, as in the previous experiment.
END
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