A little while back I did a guest blog with Scott Hanselman (a totally awesome guy - you should check out all of his stuff). It was on "EE101" - an introduction to electronics and electrical engineering - as part of the March is for Makers event. We had a grand chat as I tried to explain everything from electrons to why a motor doesn't necessarily explode when you give it more voltage than it's rated for. However, I felt there were a few things I could have explained more clearly. As such, I figured I would do a writeup covering most of the topics we covered, with some additional graphical assistance. Let's begin!
What powers our technology?
Quite simply - an electric current. That is to say, a flow of electrons from one point to another. That movement heats a filament to make a light bulb light up, creates a changing magnetic field to make a motor turn, heats up a special material to make an LED emit photons (light), etc. Moving electrons power our world.
Ok but - what causes an electric current?
Simply put, a voltage and a path. A voltage is an imbalance of electrons that wants to balance out. If you give it the opportunity, the electrons will move from point A where they are all bunched up, to point B where there are very few electrons. A voltage is a kind of potential energy, just like gravity (remember high school physics?), hence voltage's proper name - electric potential.
What limits a current?
At this point, you might intuitively guess that too much current can be a bad thing. This is true! Put the right amount of current into an LED and it lights up. Put too much and it explodes. Well, not really. But it stops working. So what determines much current flows when you have a voltage between two points and a path for electrons to flow? That would be resistance. Resistance is a term for how much opposition to current flow there is based on the material of the path (the conductor).
The water analogy
At this point, we're ready for the water analogy. The flow of water is often used to teach electricity. Think of a hose. Turning the knob is the equivalent of adding a voltage source. When you turn it on, water (electricity) wants to flow through the hose (the conductive path). But if your hose is all kinked up, water is slowed down. Those kinks are the resistance.
The relationship between voltage, current, and resistance is defined mathematically by V = I*R. V is for Voltage (measured in volts), I is for current (measured in amps) and R is for resistance (measured in ohms). This equation is known as Ohm's Law.
will get you quite far! You can put together many basic circuits with just understanding voltage, current, and resistance.
Next time I'll explain more about how these concepts and a few more enable you to use Arduinos and sensors.