Monday, February 6, 2017

Ohm’s Allegory

In science a “law” is a lesser concept than a “theory”. Theories include an explanation of why something works the way it does. For example: the theory of relativity, evolutionary theory, quantum theory, etc. But when we posit a law, all that’s required is to formalize observations of some type of effect.

Ohm’s Law relates three electrical quantities, voltage, current, and resistance. In the early 1800’s Georg Ohm measured the relationship between them (OK, not exactly, but others generalized his work to that). And it was found that Voltage equaled Current times Resistance ( V= IR). Where voltage was the amount of force (electromotive) the system had. Current then was the actual amount of electrical charge that flowed through the circuit. And Resistance was the measurement of how difficult it was to get the flow of current through the circuit.

It is the current that is what does the “work” involved in electrical theory. Since work is, in physics, the application of force over a distance. So with resistance the amount that gets done will be less.

And while high enough voltage can be disruptive, the static electricity that zaps us as we pet our dogs and cats can have high voltages, maybe up to 20,000 volts, and can annoy us and the cat, it isn’t really that dangerous. It’s the combination of voltage and current that can stop your heart.

Most of us have LED (light emitting diodes) devices all around us. They are in our flashlights, and TV remote controls, and we’re starting to switch over to LED light bulbs. And in these devices there is typically a resistor in the circuit. This resistor is called the current limiting resistor. Without it, there is a good chance that the voltage, and current through the LED, will cause the light to “burn” out.

 So to keep the light on, we need the resistor.

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