Electromagnetism Experiments
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 magnetically levitated 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.
Experiment 1: Electromagnetic Suction
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!
Materials:
drinking straw
5 feet insulated copper wire
6-volt battery
needle
Procedure:
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!
Experiment 2: Electromagnet
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:
Materials:
5 feet insulated copper wire
6-volt battery
large iron nail
paperclips
Procedure:
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?
3. Strip an inch of insulation off each end of the wire.
4. 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!
Maglev Trains
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!
Science Links
Read about NASA experiments with launching spacecraft via magnetic levitation.
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.
