Electromagnet Experiment Explanation
Onfroi Baird
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!
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 that is 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.)
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!
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.
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!
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In 1831, the great experimentalist Michael Faraday set out to prove electricity could be generated from magnetism. He created numerous experiments, including the simple but illustrious setup of the copper wire and permanent magnet . Faraday wrapped the copper wire around a paper cylinder and attached the ends of the coil to a galvanometer, which is a device that detects and measures electrical current.
To give credit where credit is due, Joseph Henry was not far behind in his independent discovery of electromagnetic induction in 1832. Dig deeper into the history of important scientists in our Pioneers section.
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Experiment 2: demonstrating the direction of magnetic field in various points around a current-carrying coil. A small compass was placed inside a coil and current was then switched on. Students could move the compass inside and around the coil during demonstration.
Experiment 4: demonstrating electromagnetic induction. The magnet was inserted in the coil, left for some time at rest inside it, and then again removed from the coil. Students were allowed to perform the experiment on their own to try different orientations or speeds of the magnet entering the coil. An additional experiment was shown using another coil with less windings than the first one.
Experiment 5: demonstrating electromagnetic induction using two coils. Primary coil with an iron core was connected to a dc supply and a secondary coil, with less windings than the primary, to the galvanometer. At first, the coils were positioned parallel to each other, and the current in the large coil was switched on and, after some time, off. The same was repeated for perpendicularly oriented coils and for coils at about 45 degrees to each other.
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An electromagnet is a magnet that can be turned on and off. In this experiment, the battery is a source of electrons. When you connect the wire to the battery, the electrons flow through the wire. If there is not a complete circuit, the electrons will not flow. Electrons behave like little magnets and when they flow through a wire, they create a magnetic field, which turns the nail into a magnet that can pick up paper clips and staples!
Wrecking yards employ extremely powerful electromagnets to move heavy pieces of scrap metal or even entire cars from one place to another. Your favorite band uses electromagnets to amplify the sound coming out of its speakers. And when someone rings your doorbell, a tiny electromagnet pulls a metal clapper against a bell.
Mechanically, an electromagnet is pretty simple. It consists of a length of conductive wire, usually copper, wrapped around a piece of metal. Like Frankenstein's monster, this seems like little more than a loose collection of parts until electricity comes into the picture. But you don't have to wait for a storm to bring an electromagnet to life.
A current is introduced, either from a battery or another source of electricity, and flows through the wire. This creates a magnetic field around the coiled wire, magnetizing the metal as if it were a permanent magnet. Electromagnets are useful because you can turn the magnet on and off by completing or interrupting the circuit, respectively.
Electromagnets differ from your run-of-the-mill "permanent" magnets, like the ones holding your Popsicle art to the fridge. As you might know, magnets have two poles: north and south. They attract things made of steel, iron or some combination thereof.
Like poles repel and opposites attract (ah, the intersection of romance and physics). For example, if you have two bar magnets with their ends marked "north" and "south," the north end of one magnet will attract the south end of the other. On the other hand, the north end of one magnet will repel the north end of the other (and similarly, south will repel south).
Superconducting magnets are a type of electromagnet that use the phenomenon of superconductivity to produce a highly strong and persistent magnetic field. It consists of coils made of superconducting materials that can carry electric currents with virtually zero resistance, allowing for a greater magnetic field strength without significant energy loss or heat generation. Meanwhile, a magnet possesses inherent magnetic properties and creates magnetic fields without the need for an external power source.
The doorbell is a good example of how you can use electromagnets in applications where permanent magnets just wouldn't make any sense. When a guest pushes the button on your front door, the electronic circuitry inside the doorbell closes an electrical loop, meaning the circuit is completed and turned on. The closed circuit allows electricity to flow, creating a magnetic field and causing the clapper to become magnetized.
The hardware of most traditional doorbells consists of a metal bell and metal clapper that, when the magnetic pull causes them to clang together, set off the chime inside. The bell rings, the guest releases the button, the circuit opens and the doorbell stops its infernal ringing. This on-demand magnetism is what makes the electromagnet so useful.
Through continued experimentation, Maxwell determined that these charges attract or repel each other based on their orientation. He was also the first to discover that magnets have poles, or individual points where the charge is focused. And, important for electromagnetism, Maxwell observed that when a current passes through a wire, it generates a magnetic field around the wire.
Maxwell's work was responsible for many of the scientific principles at work, but he wasn't the first scientist to experiment with electricity and magnetism. Nearly 50 years earlier, Hans Christian Oersted found that a compass he was using reacted when a battery in his lab was switched on and off [source: Gregory].
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