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.)
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!
What You Need:
drinking straw
5 feet insulated copper wire
6-volt battery
needle
What You Do:
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: