1. Electrical Current
Today starts the booklet on resistance.
- If current (electron movement) and electromotive force (resulting in voltage, a difference in potential throughout a circuit) are two key elements of a circuit, resistance is a third factor always present.
- "Resistance is the property that opposes current flow" (6).
- Resistance is symbolized by R and the unit is the ohm, symbolized by Ω.
- Conductors have low resistance, insulators or non-conductors have high resistance.
- Some factors that determine resistance include the nature of the material (atomic structure), the area of the cross-section (e.g., of wire), and the length (e.g., of wire). The larger the cross-section, the less the resistance. The longer the wire, the more the resistance. Atomic structure determines how many free electrons are available to move around.
- One ohm is the amount of resistance that allows 1 amp to flow through a circuit when one volt is applied. 1 amp per volt.
- Resistance is sometimes needed to limit the current flow to a safe value through a circuit. Completely unopposed current can lead to a "short circuit," which is damaging.
- The resistance of a toaster or iron or bulb is what provides the heat or light.