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. (Adult supervision recommended.)
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 and let go. What happens?
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 again to pick up the paperclips with the nail. 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!
A maglev (magnetically levitated) train doesn't use a regular engine like a normal train. Instead, electromagnets in the track produce a magnetic force that pushes the train from behind and pulls it from the front. You can get an idea of how it works using some permanent magnets and a toy car.
1. Tape a bar magnet to small toy car with the north pole at the back of the car and the south pole at the front.
2. Put the car on a hard surface, like a linoleum floor or a table. Hold a bar magnet behind the car with the south pole facing the car. As you move it near the car, what happens? The south pole of your magnet repels the north pole of the magnet on the car, making the car move forward.
3. Have someone else hold another magnet in front of the car, with the north pole facing the car. Does the car move faster with one magnet 'pushing' from behind and the other magnet 'pulling' from ahead?
In our example, the permanent magnets have to move with the car to keep it going. In a maglev track, though, the electromagnets just change their poles by changing the direction of the electric current. They stay in the same spot, but their poles change as the train goes by so it will always be repelled from the electromagnets behind it and attracted by the electromagnets in front of it!