Definition
The opposition a material offers to the flow of electric current. Resistance is measured in ohms (symbol Ω) and is represented in equations and circuit diagrams by the letter R. By Ohm's Law, the current flowing through a conductor equals the voltage across it divided by its resistance (I = E/R).
Plain English
Resistance is how hard it is for electricity to move through something. The higher the resistance, the less current flows for a given voltage. R is just the shorthand letter used for it in formulas and diagrams.
Context Anchor
Seen in aircraft electrical-system discussions, wiring diagrams, and troubleshooting of lights, radios, batteries, and other powered equipment.
Derivation
From the Latin 'resistere,' meaning 'to stand against' or 'to oppose.' That fits well — resistance is the property of a material that stands against the flow of electrons.
Why Pilots Care
Unwanted resistance causes voltage loss, heat buildup, or failure in critical systems like lights, instruments, and radios.
Analogy
Think of resistance like a narrow section in a water pipe. The narrower it is, the harder it is for water to flow through at the same pressure. In a wire, a higher R means less current flows for the same voltage.
Intuition Check
Resistance does not mean refusing an instruction here. In aircraft electrical systems, it means opposition to the flow of electric current.
Example Sentence 1
When the landing light bulb's filament aged, its resistance increased, so the light grew dimmer even though the bus voltage was unchanged.
Example Sentence 2
Corrosion raised the resistance in the battery cable and prevented a reliable engine start.