Magnetic Induction and its Relation to Magnetism
Created | Updated Jul 23, 2002
It is a well-known fact that any moving substance, be it water, wind, gerbils, or whatever, can be used to generate electricity. But how does it happen? What most people know is that the moving substance turns a shaft, the shaft turns a turbine, and the turbine makes electricity. But how?
To truly understand this concept, one must be aware of a few things. For example: magnetic charge is the product of moving electrons. Therefore, wherever there is an electron moving, there is magnetic charge. Now, several things might pop into a normal person's head at this point. One might be, 'Wait, wait, isn't that all that electricity is?' That is true. That also means, conclusively, that wherever there is an electric current, there will be a magnetic field. The next question might be: 'But aren't all things made up of atoms? And don't all atoms have orbiting electrons?' The answer to that would be 'Yes'. This is where you should pay attention.
What Magnetism Actually Is
Technically, everything can have a magnetic field1. But the reason that it doesn't show in most materials is that for the magnetic field in a substance to be effective, all the magnetic domains must be aligned. A magnetic domain is an area inside a material that has electrons and magnetic properties2. A good analogy for why these domains need to be aligned would be this:
Imagine a line of people. Ten people, to be exact. Now, these people are going to attempt to line dance. The problem here is that only a couple of people will be doing the same thing at the same time. So some people are doing the grape vine, at the same time running into those people doing the bunny hop, all of which trample the macarena people. This is chaos, and the line gets nowhere with the dance. They might not even make it outside like this. But, for a moment, imagine that all the people were moving perfectly in time. They'd have no problems finishing the dance, and probably feel so good that they'd all go out for dessert afterwards.
Now, to understand why this has any relevance whatsoever, one must compare these people to the magnetic domains. If the domains are all doing their own thing, the overall magnetic field is minute. But if all the domains are aligned in the same direction, the magnetic fields of all the domains work together, and an overall magnetic field is created.
So Why Do We Need to Know This?
The reason for this is that to properly understand magnetic induction, one must understand that magnetic fields and electrons interact. This idea will come in handy.
The Discovery of Magnetic Induction
Magnetic induction can, oddly enough, be credited to two people. In the same time period of the 1800s, both the British physicist Michael Faraday and the American High School teacher Joseph Henry began work on converting magnetism into electricity. The two worked independently, almost certainly never knowing that the other existed. Both using the results of the experiments of the Danish physicist Hans Christian Oersted3, the two worked for ten years, with innumerable failed experiments. Then, in 1832, both men made the same discovery: magnetic fields can produce electric current.
What Does It Take?
To make a basic electric current is simple. All that is needed for current to show in a wire is moving magnetic fields. It doesn't matter if it's the wire moving or the field; if the wire (or any other moveable conductor) crosses through magnetic field lines, current will be made.4. There is one important bit: if the wire is moving parallel to the field lines, no current will be made. If it moves at an angle, less current will be made. Another factor that influences the current is the direction of the movement. When the wire is moving in one direction, the current goes in one direction. When the wire reverses directions, so does the current. There is one easy way in which to tell in what direction the current is moving. Using the right hand, point a finger in the direction that the field lines are moving5, and point the thumb in the direction of the wire's movement, the palm will be facing the direction of the flow of current.
Electromagnetic Induction is the process of using magnetic fields to produce voltage, and in a complete circuit, a current. Michael Faraday first discovered it, using some of the works of Hans Christian Oersted. His work started at first using different combinations of wires and magnetic strengths and currents, but it wasn't until he tried moving the wires that he got any success.
It turns out that electromagnetic induction is created by just that - the moving of a conductive substance through a magnetic field. But, it still wasn't that simple. The process of moving the wires creates what is still called EMF, or Electromotive Force. The problem that this name poses is that it is not a force, but simply a difference in charges. In other words, it is identical to voltage in every respect. It is important to remember this, because calling it a force would be incorrect. A force is a push or a pull, and electromotive force is neither.
The obvious use for electromagnetic induction would be to generate power. Any device that does this is known as a generator. Most generators work with a small loop of wire inside a magnetic field, oriented so that it may spin and move the wire through the magnetic field lines6. This wire is connected to a turbine or some other spinning wheel, and through whatever source of energy conversion (steam, moving water, wind, etc) it spins, and generates current. But that isn't all. When a current is induced, it induces a counter-current, or 'back EMF'. Lenz's Law7states:
The direction of the induced current is such that the magnetic field resulting from the induced current opposes the change in the field that caused the induced current.
The practical upshot of all this is that when a current is induced, it produces a magnetic field opposite to what caused it. This also creates a current that moves in the opposite direction of the original current. This current causes a small bit of resistance, depending on how much back EMF is being produced.