Author: Joe H., Inflow Engineer
In the last post, we talked about what electricity is. As a quick refresher, there are tiny charged particles called electrons, and electricity is the movement of these electrons. In this post, we’re going to look more closely at the relationship between electricity and magnets, and how magnets can be used to generate electrical currents. We’ll start with a closer look at magnets and something called electromagnetic fields.
Almost everyone has played with magnets at some point in their life. Every magnet has two ends, typically labelled N and S. If you take one of these magnets and place it in a pile of iron filings, the iron filings will move themselves around into the pattern as seen in Figure 1.
Figure 1: Magnetic Field
These lines are a physical manifestation of the electromagnetic field that exists between the N and S ends of the magnet. This field is caused by the arrangement of electrons (and the atoms they’re attached to) within the magnet. Field theory is a very complex topic, but for our purposes we can think of them as the lines along which a force moves. A force is anything that pushes or pulls something else. For example, gravity is the force that pulls objects with mass together . The force that we’re interested in here is the electromagnetic force, which is the force which pushes and pulls charged particles.
In the case of magnets, the electrons in the iron filings are pulled into alignment with the field lines by the electromagnetic force, pulling the filings along with them. Any time you have an electromagnetic field and you put electrons in that field, the electrons will be pushed into alignment with the field by the electromagnetic force. Since electrons move to align themselves with these types of fields, when you move an electromagnetic field across a metal wire by moving the magnet generating the field, the electrons in that wire will move just like the electrons in the iron filings. If the wire isn’t allowed to move with them, the electrons will move from atom to atom in an attempt to align with the field, causing a uniform flow of electrons in one direction within the wire. This movement will in turn displace other electrons in the parts of the wire not placed into the electromagnetic field, causing an electrical current to move down the whole length of the wire. If the ends of the wire are disconnected, there’s nowhere for the electrons to go, but as soon as the ends are connected, the current will be able to flow freely. When you move the magnet in one direction, the current will flow in one direction, and when the magnet moves back in the other direction, the current will flow in the opposite direction. Imagine a tube filled with metal marbles, connected to form a circle. If you move a magnet along the tube, all the marbles will move, while the tube itself will remain stationary. In the same way, we generate electrical current by spinning magnets (using a steam turbine or water turbine for example) within wire loops, as shown in Figure 2.
Figure 2: Basic Generator 
All the electricity we use in our modern world is generated this way. There are other natural phenomena which can create electrical currents, such as static electricity, but they don’t create consistent, controllable currents. By using magnets, we can make electrons move in predictable, consistent ways. If you have a magnet of a given strength and you spin it at a consistent speed inside a specific wire loop, you will always get the same number of electrons moving. This is important if we’re trying to design a device that does certain things based on how many electrons are flowing through it. For example, a light bulb connected to an inconsistent power source will flicker out if it does not receive enough electrons and could burn out if it receives too many electrons.
So now we have established a way to move a specific number of electrons at a given speed, we can use batteries to store these electrons for later use or we can start designing things that use those electrons to do something. The first thing we need in order to do this type of design is a way to describe how many electrons and therefore how much current is moving across an area. The unit we use is amperes or amps. One ampere is approximately 6,242,000,000,000,000,000 electrons worth of charge moving past a point per second. In the next post, we’re going to look at what happens when you push that many electrons through a wire, so be sure to check back for that!
 Technically, gravity bends spacetime itself, but that’s outside the scope of this post series. For more on gravity from a general relativity perspective, check out this video from PBS Space Time.
 By Egmason - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=1025045
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