## Friday, August 7, 2009

### Basic electronics - Inductors and Inductance

Right, we've done a little bit so far on resistors, capacitors and diodes, so today we're going to move on to Inductors and Inductance to help us with that huge chunk of section A, those 12 questions which we need to know this stuff for.

After a quick Google search, I came up with a website that seems to explain things in very simple language. The website is howstuffworks.com. Here is a direct quote from that website:

An inductor is about as simple as an electronic component can get -- it is simply a coil of wire. It turns out, however, that a coil of wire can do some very interesting things because of the magnetic properties of a coil.

Great. So an inductor is a coil of wire. Simple eh?

An inductor is an electromagnet. An inductor resists a change in the flow of electrons. You can think of an inductor in terms of a large water wheel with its paddles dipping into a narrow water channel.
Now you try to start the water flowing. The paddle wheel will tend to prevent the water from flowing until it has come up to speed with the water. If you then try to stop the flow of water in the channel, the spinning water wheel will try to keep the water moving until its speed of rotation slows back down to the speed of the water.
The capacity of an inductor is influenced by four things:

* The number of coils - More coils means more inductance.
* The material that the coils are wrapped around (the core)
* The cross-sectional area of the coil - More area means more inductance.
* The length of the coil - A short coil means narrower (or overlapping) coils, which means more inductance.

The Unit of Inductance is the Henry.

It would be helpful at this point to look at Faraday's Law (remember him, and the unit of capacitance, the Farad?)

Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil. No matter how the change is produced, the voltage will be generated. The change could be produced by changing the magnetic field strength, moving a magnet toward or away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to the magnet, etc.

To help us further understand what an inductor does, we'll look up the word inductance in the dictionary:

that property of a circuit by which a change in current induces, by electromagnetic induction, an electromotive force.

So we're getting the picture. Let's just have a look at the IRTS disk before moving on to the next subject.

Any wire carrying a current is surrounded by a magnetic field; winding the wire into a coil strengthens this field
•When the current changes, the magnetic field changes inducing a back emf in the coil that opposes the change in current. This phenomenon is called self inductance
•The unit of inductance is the Henry (H) but as this is a large unit the milli- and micro-Henry (mH, mH) are more commonly used

OK, we're going to let that sink in because there's a wee bit more to study on inductors before we move on.