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What's the difference between a lightning bolt and a refrigerator magnet? Perhaps there's much less difference than you think! Thanks to the discoveries of Michael Faraday and James Clerk Maxwell in the mid-1800s, we now know that electricity and magnetism are just two facets of the same principle.
One of the main principles behind electricity and magnetism is that the movement of charged particles in the same direction will result in a magnetic force. When a wire is hooked up to a battery, negatively charged particles (electrons) flow away from the negative terminal of the battery toward the positive end, because opposite charges attract each other, while like (similar) charges repel each other. This flow of electrons through wire is electric current, and it produces a magnetic force. In a magnet, atoms are lined up so that the negatively charged electrons are all spinning in the same direction. Like electric current, the movement of the electrons creates magnetic force. The way the atoms are lined up creates two different poles in the magnet, a north pole and a south pole. As with electrical charges, opposite poles attract each other, while like poles repel each other.
Electric current flowing through a wire creates a magnetic field that attracts ferromagnetic objects, such as iron or steel. This is the principle behind electromagnets and magnetic levitation trains. It allows cranes to pick up whole cars in the junkyard and makes your doorbell ring. You can read about it here, and then watch it work when you do these experiments.
A single strand of wire produces only a very weak magnetic field, but a tight coil of wire (called a solenoid) gives off a stronger field. In this experiment you will use an electric current running through a solenoid to suck a needle into a straw!
1. Make your solenoid. Take five feet of insulated copper wire and wrap it tightly around the straw. Your solenoid should be about 3 inches long, so you'll have enough wire to wrap a couple layers.
2. Trim the ends of the straw so they just stick out of the solenoid.
3. Hold the solenoid horizontally and put the end of the needle in the straw. What happens? (Nothing!)
4. Now strip an inch of insulation off each end of the wire and connect the ends to the 6-volt battery. Insert the needle part-way in the straw again and let go. This time what happens? (Don't leave the wire hooked up to the battery for more than a few seconds at a time - it will get hot and drain the battery very quickly)
When you hooked your solenoid up to a battery an electric current flowed through the coils of wire creating a magnetic field. This field attracted the needle just like a magnet and sucked it into the straw. Try some more experiments with your solenoid - will more coils make it suck the needle in faster? Will it still work with just a few coils? Make a prediction and then try it out!
As you saw in the last experiment, electric current flowing through a wire produces a magnetic field. This principle comes in very handy in the form of an electromagnet. An electromagnet is wire tightly wrapped around a ferromagnetic core. When the wire is connected to a battery, it produces a magnetic field that magnetizes the core. The magnetic fields of the core and the solenoid work together to make a very strong magnet. The best part about it is that the magnetic force stops when the electricity is turned off! Try it yourself with this experiment:
1. Tightly wrap the wire around the nail to make a solenoid with a ferromagnetic core. If you have enough wire, wrap more than one layer. (If your nail fits inside the straw from the last experiment, you can use that solenoid instead of rewrapping the wire.)
2. Try to pick up some paperclips with the wire-wrapped nail. Can you do it?
2. Strip an inch of insulation off each end of the wire.
3. Hook up the wire to the battery and try to pick up the paperclips with the nail again . This time the electricity will create a magnetic field and the nail will attract paperclips! (Don't leave the wire hooked up to the battery for more than a few seconds at a time - it will get hot and drain the battery very quickly.)
Experiment some more with your electromagnet. Count how many paperclips it can pick up. If you coil more wire around it will it pick up more paperclips? How many paperclips can you pick up if you only use half as much wire? What would happen if you used a smaller battery, like a D-size? Predict what you think will happen and then try it out!
Imagine riding on a flying train at speeds of up to 310 miles per hour - does that sound like science fiction? Well, it isn't! Such a thing exists, and it is called a maglev (magnetically levitated) train. Maglev trains move at unprecedented speeds because they avoid the friction of wheels on a track. Instead, strong electromagnets in the track repel magnets on the underside of the train, causing the train to "float" just above the track. You can visualize this with some ring magnets and a pencil. Hold the pencil vertically with the eraser touching a table. Slide the magnets onto the pencil one at a time, with like poles facing each other. The magnets will repel each other and "float." (If they stick together, turn one over.)
A maglev train uses magnets to float above the track, but it also uses magnets to propel it forward instead of running off a regular fossil-fuel-powered engine. The electromagnets in the track continually change their poles by alternating the direction of the electric current. The changing poles cause the magnetic field in the track to pull (attract) the train from the front and push (repel) it from behind.
Maglev technology is still developing, and the trains aren't yet in common use. (Besides, they're very expensive!) But a German-built maglev train was opened to the public in 2003: it takes passengers from downtown Shanghai, China to the airport - 19 miles - in just eight minutes. By taxi the same trip takes an hour!
Polar Nicknames. If you hang a bar magnet from a string, it will settle so that its north pole points toward the magnetic north pole of the earth. But how can this be if like poles repel each other? The truth is that we just call the poles on a magnet "north" and "south" for short. Their full names are the "north-seeking pole" and the "south-seeking pole." The north-seeking pole is the true south pole of the magnet - it is attracted by the north pole of the earth.
Super Strong. Some magnets are called "rare earth magnets," not because they are rare, but because they are made from elements in the rare earth group on the periodic table (elements #57-103). These magnets are very strong. A neodymium disc magnet only 1/2" in diameter can lift over 7 pounds of ferromagnetic material!
Use this animated, interactive lesson to teach your young children about magnetism.
Find intermediate to advanced magnetism projects at the Exploratorium's Science Snacks page.