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Electricity 102

Resistance and Capacitance

In my earlier ramblings (Electricity 101 - Voltage, Amperage and Power) I bored you half to death about the basic principles of electricity. If you were able to follow at all you may have noticed 2 things I mentioned. First thing was Resistance. Resistance is simply something in the path that slows the flow of electrons (Current). It does not reduce the number of electrons delivered (Voltage). Before any smartasses snapp at me telling me "wanna bet? I can show you how Resistance can reduce electrons", yea yea I know. Resistance *can* reduce the number of electrons in a circuit, but the initial introduction of Resistance in the path simply slows the rate. We will get into using Resistance to reduce the number of electrons later as it is a bit more complex and to be honest, most people don't remember much about fractions and matrices unless they work with them often.

So from the start Resistance is equal to Voltage divided by the Current, or R = V/I which simply means that the Voltage is traveling across the path, let's say 12VDC. A form of Resistance is introduced into the path. After the Resistance, the Current is measured at 2A. This means that R = 12V/2A so R = 6. 6 what? 6 Resistance? No. 6 Ohms. 6 WHAT??? Ohms. Named after a Physicist over a hundred years ago. Ohms are the measure of electrical Resistance. It is representated by the greek symbol Omega Ω so 6 Ohms would be expressed as 6Ω. So R = 12V/2A = 6Ω - got it? So what does a Resistor actually do? A Resistor actually slows the flow of the Current. This does not change the quantity of electrons, it just slows them down.

So now as mentioned earlier I said that a Resistor only slows the current and does not change the Voltage. Then I held back from saying that it can change the Voltage as well. Actually it cannot change the Voltage but let's think about this. If the train (yup back to the train) is on a path and the path splits, does the train decide which path to take? Actually no. The train is not a single consistent object. It flows freely as water does. So if water in a pipe flowing now sees a split in its path it travels down both paths. The flow rate remains the same but the Voltage now drops between the 2 paths. The problem here is stability. Why would we do this? Well some of the Current needs to be returned to the source, but we need to control how fast it is returned in order to control the actual Voltage going into the circuit. So first we add a Resistor to the initial path in order to control the entry flow rate, then the split. Path 1 goes to the circuit and path 2 goes to another Resistor (called a load) to control the return rate, then back to the source. So yes a Resistor *can* be used to lower Voltage but the Resistor itself does not perform this function.

Now what if a part of the circuit needs a bit more Voltage than others, the input Voltage simply will not do. So instead, we have a component whose job it is to just collect little tidbits of electrical charges and release them when they are done collecting just the right amount of charge. This collector essentially fills itself to capacity, so we call it a Capacitor. It's designed specifically to collect charges from the circuit and release it when it reaches the desired amount of charge. So in order to understand how much electrical charge a Capacitor can hold, we measure the container in Farads, named for yet another famous scientist, Michael Faraday. Faraday proposed that a single charge is the same as a single Coulomb. A what? A Coulomb. Huh? Dude, a Coulomb! It's a representative standard number used to represent 6.2415x1018 electrons. So in other words, 6,241,509,744,511,500,288 electrons. So 1 Farad is that many electrons, or a single Coulomb. So Farads and Coulombs are they same? No. A Farad is stored charge and a Coulomb is a measurement of 1 Amp per second.

Right I went off the deep end and I am not sorry. It's like this. 1 Amp is rated over a period of an hour. So that would be called an Amp-hour (or Ah). 1 Coulomb is measured as 1 Amp per second. It's measured over a smaller period of time. A Farad is measuring how many Coulombs are being collected. It has no time difference or deviation, it just collects until it's full then releases the charge to the circuit. Basically it's like a battery but rather than discharging at a slow and consisten rate, a Capacitor releases all at once. Not over the period of an hour, not over a minute or a second. It releases the charge at the speed of light. Capacitors are rated up to a maximum Voltage so anything higher, well we already discussed that. Too many electrons at once can be bad. A night club has a max capacity of 100 persons. A small club obviously. Go over that amount and things could get really bad. Well same thing with electrons and capacitors. Think about it. You already have 6.2415x1018 electrons in each Coulomb (or charge) and 1 V = 1 J / C. Again not sorry. J is Joule and a Joule is 1 electron Volts (eV).

It seems all so redundant I know but as we go on in the ramblings, I'll explain a bit more. Too much information all at once will eventually burn you out. I've been learning this stuff since 1976 and to be honest, things were much simpler when I was younger. You learn a little bit at a time as it applies to what you need and boom, it all clicks. Too much at once and it's just jumble crap floating about that makes no sense. "So what good is all this crap if I don't know what it's for or how to use it?" Sure easy answer. Typical LED bulbs need 3VDC. I have a hand-wound generator. For every turn it delivers a charge. Since I am winding by hand, I see that the voltage varies from 1.2VDC to 4 VDC. Remember too many Volts will damage a circuit. An LED can easily be damaged, but this difference is neglegible and the LED should be okay. So I connect the hand wind to the LED and start cranking. The LED start lighting up but it's flickering. Why? My cranking skills simply suck. So how do I make it flicker less? Well if I can store a charge and pass it, the light will be more consistent. So I put a Capacitor in the path of the LED and viola! The flickering is reduced. So how do I get rid of the flickering altogether? Winding by hand? Nah, not gonna happen. But if the variance of Voltage were predictable, I strategically place a number of Capacitors in the path larger at first, then reducing down so I collect more at first and release less as I get closer to the LED. The amount of charge becomes more consistent as it is released to the LED and that should reduce the flicker.Again think of a water pipe. A large collector from the "unstable" source to collect as much as possible, then release it to a smaller collector to offer a more smooth release to the LED. This will produce a smooth stream of water to the spout.

So can a Resistor and Capacitor work together in any way? Oh sure! They are often paired/partnered together to create a smoother flow path for electricity to travel in circuits. The more complex a circuit, the more you will see them working together.


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