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| Flow of Electric Current |
"Electrical Resistance" is defined as the "characteristics of the material that impedes the flow of electricity through the material." Even the best electrical conductors, (i.e. Gold) have some resistance to the flow of electricity (electrons) through them. Think of Resistance as a measure of how loosely or tightly a material holds onto its electrons. Materials that allow their electrons to move easily (conductors) have “low resistance to the flow of electricity” and materials that hold tightly to their electrons (insulators) have “high resistance to the flow of electricity”.
The Electrical Resistance of a material is measured/quantified in units called "ohms". The lower the Resistance of a material in ohms, the better the material acts as a conductor. For example, Copper has a lower Electrical Resistance than Aluminum so Copper is the better Conductor. The "resistance value" for most materials can be looked up in physics or science books. In this manner, by comparing the “Ohm Value” of copper to aluminum, it can be determined how much better copper is as a conductor compared to aluminum.
We can use Resistance to flow in a water piping system as an analogy. The Resistance in the Water Pipe to the flow of water comes mainly from the size of the pipe, rust and corrosion inside the pipe, and the number of "bends" and fittings used which all add up to increase the Resistance to the flow of water through the pipe. The more resistance to the flow of water through the pipe, the bigger the pressure loss when moving water through the pipe.
The same is true of current flow in an electric circuit. The Resistance to flow in an electrical circuit comes from factors including the material the wire is made of (and impurities), the diameter of the wire, and the length of the wire.
* Aluminum Wires have more Resistance than Copper Wires for the same diameter and length.
* Smaller Wires have more Resistance than larger diameter Wires for the same material and length.
* Longer Wires have more Resistance than shorter Wires for the same material and diameter.
 | Resistance Factors |
When electricity flows through any Resistance, energy is dissipated in the form of heat. If the heat becomes intense enough, the conductor/wire could become hot enough to "glow". This is exactly how an incandescent light bulb works. The filament of the light bulb is made of a material that will resist the current enough to heat up and "glow".
The scientific symbol for Electrical Resistance, which is measured in "Ohms," is the Greek letter "Omega". Electricians and practical Wiring Books typically use an "R" to represent Resistance. So in this course, we shall use the practical symbol "R" to represent Resistance in "Ohms".
