Electrical Resistance

Flow of Electric Current

"Electrical Resistance" is defined as the "resistance to flow of electricity through a material." Even the best Conductors, (i.e. Gold) have some Resistance. Resistance Elements essentially fall somewhere between a Conductor and an Insulator. Resistance can also be considered a measurement of how tightly a material holds onto its Electrons.

The Electrical Resistance of a material is measured in units called "ohms." The lower the Resistance of a material, the better the material acts as a Conductor. For example, Copper has a lower Electrical Resistance than Aluminum; Copper is a better Conductor. The "resistance value" for most materials is listed in physics or science books. For example, "Common Resistance Elements" in a Circuit are: lights, motors, and electrical resistance headers.

We can use 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, objects stuck inside the Pipe, and the number of "bends" and Fittings all add up to increase the Resistance to the flow of water.

The same is true of current flow in an Electric Circuit. A number of factors determine the Resistance to current flow such as Wire diameter, Wire length and any impurities in the Wire's makeup. For example, smaller Wires have more Resistance than larger diameter Wires and longer Wires have more Resistance than shorter Wires.

Resistance Factors

When electricity flows through any Resistance, energy is dissipated in the form of heat. If the heat becomes intense enough, the Conductor Resistor may actually "glow". This is exactly how an Incandescent Light Bulb works. The Filament 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".