How Electromagnets Work

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).

An electromagnet is the same way, except it is temporary — the magnetic field only exists when the electric current flows. You can determine the strength of a magnetic force by adjusting the current flowing through the electromagnet.

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.

The field of electromagnetism attracted many brilliant minds over the course of several decades. Here are four individuals who made some of the most important discoveries.

James Maxwell

The relationship between electricity and magnetism wasn't thoroughly studied until 1873, when physicist James Maxwell observed the interaction between positive and negative electrical charges.

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.

Hans Christian Oersted

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].

This would only happen if there were a magnetic field present to interfere with the needle of the compass, so he deduced that a magnetic field produced electricity from the battery. But Oersted gravitated toward the field of chemistry and left the research of electricity and magnetism to others [source: Mahon].

William Sturgeon

William Sturgeon is another scientist who experimented with electromagnets. He created one of the first practical electromagnets in 1824, which consisted of a horseshoe-shaped iron core wrapped with multiple turns of wire.

Michael Faraday

And then there’s the granddaddy of electromagnetism: Michael Faraday, a chemist and physicist who architected many of the theories later built upon by Maxwell.

One reason Faraday is so much more prominent in history than Maxwell or Oersted is that he was such a prolific researcher and inventor. He is widely heralded as a pioneer in electromagnetism, but he is also credited with discovering electromagnetic induction.

Faraday also invented the electric motor, and besides his influential work in physics, he was the very first person to become appointed the prestigious position of Fullerian Professor of Chemistry at the Royal Institution of Great Britain.

Basic electromagnets aren't all that complicated; you can construct a simple one yourself using materials you probably have lying around the house.

OK, there's a little more to it than that.

Tightness of the Winding Wire

The tighter the wire wound around the rod, or core, is, the more loops the current makes around it, increasing the strength of the magnetic field.

Core Material

In addition to the tightness of the winding wire, the material used for the core can also control the strength of the magnet. For example, iron is a ferromagnetic material, meaning it is highly permeable [source: Boston University]. Permeability is another way of describing how well the material can support a magnetic field. The more conductive a certain material is to a magnetic field, the higher its permeability.

Electric Current

All matter, including the iron rod of an electromagnet, is composed of atoms. Before the solenoid is electrified, the atoms in the metal core are arranged randomly, not pointing in any particular direction. When there is a current, the magnetic field penetrates the rod and realigns the atoms.

With these atoms in motion, and all in the same direction, the magnetic field grows. The alignment of the atoms, small regions of magnetized atoms called domains, increases and decreases with the level of current, so by controlling the flow of electricity, you can control the strength of the magnet. There comes a point of saturation when all of the domains are in alignment, which means adding additional current will not result in increased magnetism.

By controlling the current, you can essentially turn the magnet on and off. When the current is turned off, the atoms return to their natural state (meaning in random directions), and the rod loses its magnetism. (Technically, it retains some magnetic properties but not much and not for very long).

With a run-of-the-mill permanent magnet, like the ones holding the family dog's picture to the refrigerator, the atoms always align, and the strength of the magnet is constant. Did you know that you can take away the sticking power of a permanent magnet by dropping it? The impact can actually cause the atoms to fall out of alignment. You can magnetize them again by rubbing a magnet on it.

Since you need an electrical current to operate an electromagnet, where does it come from? The quick answer is that anything that produces a current can power an electromagnet. From the small AA batteries used in your TV remote to large, industrial power stations that pull electricity directly from a grid, if it stores and transfers electrons, then it can power an electromagnet.

Let's start with a look at how household batteries function. Most batteries have two easily identifiable poles, a positive and a negative. When the battery isn't in use, electrons collect at the negative pole. When you insert the batteries into a device, the two poles come into contact with the sensors in the device, closing the circuit and allowing electrons to flow freely between the poles.

In the case of your remote, the device is designed with a load, or exit point, for the energy stored in the battery. The load puts the energy to use operating the remote control. If you were to simply connect a wire directly to each end of a battery with no load, the energy would quickly drain from the battery.

While this is happening, the moving electrons also create a magnetic field. If you take the batteries out of your remote, it will likely retain a small magnetic charge. You couldn't pick up a car with your remote, but maybe you can pick up some small iron filings or even a paper clip.

On the other end of the spectrum is the Earth itself. An electromagnet results when electrical currents flow around some ferromagnetic core. The Earth's core is iron, and we know it has a north pole and a south pole. These aren't just geographical designations but actual opposing magnetic poles.

The dynamo effect, a phenomenon that creates massive electrical currents in the iron thanks to the movement of liquid iron across the outer core, creates an electrical current. This current generates a magnetic charge, and this natural magnetism of the Earth is what makes a compass work. A compass always points north because the metal needle is attracted to the pull of the North Pole.

Many electromagnets have an advantage over permanent magnets because they can be easily turned on and off, and increasing or decreasing the amount of electricity flowing around the core can control their strength.

Electronics

Modern technology relies heavily on electromagnets to store information using magnetic recording devices. When you save data to a traditional computer hard drive, for example, tiny, magnetized pieces of metal are embedded onto a disk in a pattern specific to the saved information. This data started life as binary digital computer language (0s and 1s). When you retrieve this information, the pattern is converted into the original binary pattern and translated into a usable form.

So what makes this an electromagnet? The current running through the computer's circuitry magnetizes those tiny bits of metal. This is the same principle used in tape recorders, VCRs and other tape-based media (and yes, some of you still own tape decks and VCRs). This is why magnets can sometimes wreak havoc on the memories of these devices.

You may use electromagnetism every day if you charge a phone or tablet wirelessly. The charging pad creates a magnetic field. Your phone has an antenna that syncs with the charger, allowing a current to flow. As you may imagine, the electromagnetic coils inside devices like these are small, but larger coils can charge larger devices such as electric cars.

Electrical Outlets

Electromagnets also paved the way for really harnessing the potential of electricity in the first place. In electrical appliances, the motor moves because the current flowing from your wall socket produces a magnetic field. It's not the electricity itself powering the motor, but the charge the magnet creates. The force of the magnet creates rotational movement, which means it rotates around a fixed point, similar to the way a tire rotates around an axle.

So why not skip this process and just use the outlet to power the motor in the first place? Because the current required to power an appliance is quite large. Have you ever noticed how turning on a large appliance such as a television or a washing machine can sometimes cause the lights in your home to flicker? This is because the appliance is drawing a lot of energy initially, but that large amount is only needed to get the motor started. Once that happens, this cycle of electromagnetic induction takes over.

Particle Accelerators

From household appliances, we're moving up to some of the most complex machinery ever built to see how electromagnets are being used to unlock the origins of the universe. Particle accelerators are machines that propel charged particles toward one another at incredibly high speeds in order to observe what happens when they collide. These beams of subatomic particles are very precise and controlling their trajectory is critical so they don't go off course and damage the machinery. This is where electromagnets come in. The magnets are positioned along the path of the colliding beams, and their magnetism is actually used to control their speed and trajectory [source: NOVA Teachers].

Not a bad resume for our friend the electromagnet, huh? From something you can create in your garage to operating the tools that scientists and engineers are using to decipher the origins of the universe, electromagnets have a pretty important role in the world around us.

Electromagnets are easy to make; just a few pieces of hardware and a power supply gets you on your way. First, you'll need the following items:­

Once you have these items, remove the insulation from each end of the copper wire, just enough to provide a good connection with the battery. Wrap the wire around the nail; the tighter you can wrap it, the more powerful the magnetic field will be.

Finally, connect the battery by attaching one end of the wire to the positive terminal and one to the negative terminal (it doesn't matter which end of the wire gets paired with which terminal). Presto! A working electromagnet [source: Jefferson Lab].

Can't get enough of hands-on electromagnetic experiments? We have some more ideas for you to try:

What is the magnetic power of a single coil wrapped around a nail?

Of 10 turns of wire? Of 100 turns? Experiment with different numbers of turns and see what happens. One way to measure and compare a magnet's "strength" is to see how many staples it can pick up.

What is the difference between an iron and an aluminum core for the magnet?

For example, roll up some aluminum foil tightly and use it as the core for your magnet in place of the nail. What happens? What if you use a plastic core, like a pen?

What about solenoids?

A solenoid is another form of electromagnet. It's an electromagnetic tube generally used to move a piece of metal linearly. Find a drinking straw or an old pen (remove the ink tube). Also find a small nail (or a straightened paper clip) that will slide inside the tube easily.

Wrap 100 turns of wire around the tube. Place the nail or paper clip at one end of the coil and then connect the coil to the battery. Notice how the nail moves?

Solenoids are used in all sorts of places, especially locks. If your car has power locks, they may operate using a solenoid. Another common thing to do with a solenoid is to replace the nail with a thin, cylindrical permanent magnet. Then you can move the magnet in and out by changing the direction of the magnetic field in the solenoid.

Please be careful if you try placing a magnet in your solenoid, as the magnet can shoot out.

How do I know there's really a magnetic field?

You can look at a wire's magnetic field using iron filings. Buy some iron filings or find your own iron filings by running a magnet through playground or beach sand. Put a light dusting of filings on a sheet of paper and place the paper over a magnet. Tap the paper lightly and the filings will align with the magnetic field, letting you see its shape!

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.