Power, resistance is futile

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I promised yesterday I'd try and help you understand the difference between resistance and impedance. It's useful to learn the distinction between the two because understanding their differences lends insight into the limitations of power delivery and how filters work. Resistance does what its name suggests: it resists. In the case of both electricity and water, it holds back their flow, restricting forward movement like bumper to bumper traffic in a construction zone. Nothing you can do will change the number of cars traveling the road in a given period of time, and resistors place fixed limits on flow too. Wire is a resistor. For every foot of wire, there is a fixed amount of resistance. Only so much power can flow at any one time. Same with a water pipe. A smaller diameter pipe restricts water flow more than a larger diameter pipe. The same is true for wire; the larger the diameter, the lower the resistance. But wire, unlike pipes, has a neat trick. When it gets close to another wire, or even close to itself, something strange happens. Its resistance changes. Let's use an analogy to help us see what this is like. Imagine you're driving along a deserted stretch of two-lane highway and you're the only car on the road. You're cruising along at 60 mph and it's a clear, still morning. Set the cruise control, kick back and enjoy the scenery, your engine purrs at a constant rate. As you approach town, traffic picks up and before you know it there's hundreds of cars going in both directions. This is an old two-lane highway and your flow of cars is less than a foot from the opposing lane, and your motor struggles to keep up the speed. You find yourself battling the opposing force of cars heading in the opposite direction. A line of big trucks blasts by and you really notice the resistance; your car shuddering as they pass. Suddenly, there's a construction zone up ahead. Traffic in both directions slows to a crawl and the resistance you felt at high speeds now seems gone. The car's speed picks up again and the lanes split apart; a wide empty area keeps opposing traffic away from you. It's smooth sailing again. Even at 60 mph in close traffic, there's no resistance felt because the lanes are far apart. It isn't a lot different for electricity traveling along wires. Put two conductors closely together, or just take the wire and twist it into a coil of many close loops, and this same effect happens: the faster the electricity travels down the wire, the more resistance it runs into from its near neighbor. Like our traffic example, slow down the rate at which the electricity travels and the resistance ebbs away to nothing but the friction of the road and tires. This changing resistance with frequency is called impedance. Resistance to electric flow is constant and found, in degrees that vary with material and thickness, in every conductor. Impedance is resistance that changes with the speed, or frequency, of electricity. The faster the electricity tries to go, the more resistance it runs into. Like a Chinese finger trap, there's no escape. The harder you pull, the more trapped you become–but relax and slow down, you're free of resistance. Same for electricity. The faster it tries to move, the more resistance that stops it. Lastly, when I refer to the "speed" of electricity I do not mean the exact definition that word conveys. I used "speed" only to help illustrate simply. The correct word is "frequency" and when we are referring to frequency, then we can accurately use the term "speed". And it is simple to see why. Our subject of power is based on what comes out of our homes wall sockets, not that of a battery. What comes out of the wall socket is AC. AC is simply battery voltage making quick round trips down wires: switching between + and - at a given speed. What comes from power lines is either 50 or 60 times a second. 'Nough for today.
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Paul McGowan

Founder & CEO

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