Moving electric charges create magnetic fields in the space around them. We can use these magnetic fields to generate magnetic forces. Oppositely, when we change magnetic fields around charges we can create moving electric charges, or electricity. We call both of these phenomena electromagnetism. Incredibly useful, there are devices in everyday life that use electromagnets and electromagnetism. Created by Khan Academy.
- [Instructor] You know what a magnet is, but did you know that some magnets can be turned on and off? One type of temporary magnet is called an electromagnet. So what is electromagnetism? Well, the hint is in the name itself. Electro for electrical, and magnet for, well, magnet. Let's take a moment to look at the definition of what an electromagnet is. Electromagnets are materials that become magnets in the presence of electricity. But how does that even happen? Well, it turns out that electrically-charged particles in motion actually have small magnetic fields around them. So, if we run electricity through a wire, a magnetic field will be created around the wire. Now, we can control the strength of this magnetic field in a couple of ways. We can move more electric charges through the wire at a faster rate, and we do this by increasing the electrical current. The second way is to increase the density of the charged particles, and we can do this by looping the wire into a coil. This gives us more charged particles with magnetic fields in a small space, strengthening the magnetic force. The other thing we can control with electromagnets is the direction of the magnetic field, and we can do this by changing the direction of the electricity. So if we go back to this wire example from earlier and change the direction of the electricity running through that wire, well, the magnetic fields will also change direction. This makes electromagnets quite different from permanent magnets. So let's take a look at that and compare permanent magnets to electromagnets. Electromagnets are typically made of loops of wire and a coil. The wire is typically made of metal like copper and wrapped around pieces of metal like iron, nickel, or cobalt. This is different from a permanent magnet because permanent magnets don't need this wire. Permanent magnets also have fixed poles. You can't change the north and south poles on these magnets, but as we now know, for electromagnets, we can change these poles by changing the direction of the electrical current. So, if we have an electromagnet with a north and south pole that looks like this and a current flowing in this direction, well, we can change the poles and the direction of the current. Permanent magnets have a fixed strength, but we just talked about how we can change the strength of electromagnets, so electromagnets have adjustable strength. And finally, electromagnets need a power source in order to generate the electricity required to produce magnetic fields. Permanent magnets do not need a power source, but this means that we can also turn electromagnets on and off, which is pretty cool when you think about it. On the other hand, permanent magnets are always on. Now, you might be thinking if electrical charge can affect magnetism, can magnetism affect electrical charge? Absolutely, let's look at how we can do that. The only way to do this is by changing the magnetic field around the charged particles. This can be done by moving magnets closer or further away from the particles or by spinning the magnets. In fact, spinning magnets is how most of the electricity we use in cities and homes is generated. A turbine spins a magnet inside a coil to produce electricity, and since electromagnets need a power source, this turbine is powered by wind. So you can see why electromagnetism is an incredibly important force, and this isn't the only important application of it. We use electromagnets in all sorts of other applications, from motors to speakers and even medical scanners.