This is a topic that’s only related to computers in a technically-speaking way, but I was thinking about it a lot recently and thought it might be interesting for people.
The topic is electricity. All of our cool gizmos would be useless without it. It can be dangerous and it can be beautiful. Many aspects are misunderstood as well. We use terms like “high voltage” to denote danger, but what does that mean? We have safety procedures for dealing with laptop batteries, but why do we have those?
I can’t write everything there is to know about electricity in a single article, but hopefully I can give an understanding of the basics and maybe elaborate in future Kibbles articles. I had a high school teacher that used to say Newton’s second law (Force = Mass x Acceleration) could be used to derive almost everything in physics. In the world of electromagnetism, I think of Ohm’s law the same way. Ohm’s law can be expressed as I = V/R (Current = Voltage ÷ Resistance). In any electrical system, the current, voltage and resistance are always related together by this formula.
Current is generally expressed in amperes or amps. One ampere is equal the flow of one coulomb of charge per second. A coulomb is a unit of charge. Basically one coulomb is some fixed amount of “charge”. So when we talk about amps, we’re literally talking about how much charge is passing through some point per unit of time. It takes surprisingly few amps to kill a human. Between 0.01 and 0.1 amps will cause a painful shock, labored breathing, and muscular paralysis. Between 0.1 and 0.2 amps will cause ventricular fibrillation of the heart which will result in death. Surprisingly, currents above 0.2 amps will cause heart muscle contractions so severe that the heart is effectively clamped which will actually protect it. Of course at those higher currents, burns and stopped breathing become major issues as well.
How much current is 0.1 amps? Very, very, very little. I’ve built lots of electronic projects over the years and low currents like that have very specific applications. Lower amperages can be found in digital circuits, LEDs, basically anything that relies more on voltage potentials. Transistors are good at this, hence why digital circuits tend to have fewer amps running through them. Stuff that ??does?? stuff, like motors, solenoids, heaters, etc, draw far more amps. We have a small 8-inch desk fan in our server room that draws about 0.4 amps on high.
If so few amps can cause death, why am I not shaking in fear of this formidable desk fan in our server room? It’s just sitting there waiting to kill me! Someone, quick, call the police! The reason is because of Ohm’s law and the role that resistance and voltage play in relation to current. Join me next week when I talk about voltage, how it creates current, and why resistance is far from futile.
