Resistance, up close

Resistance opposes current flow and is measured in ohms. Ordinary wires have some resistance; superconductors under suitable conditions are an exception. A resistor is designed to provide a specified resistance within stated tolerances and operating conditions.

The rule is straightforward: for a fixed voltage, higher resistance means less current. It’s the narrow-straw effect — forcing water through a thin, long straw is hard work, while a short, wide pipe lets it gush. Thin and long wires resist more; thick and short ones resist less.

Resistance also turns electrical energy into heat. That is sometimes the goal (a toaster, a heater, an old-style bulb) and sometimes a nuisance (a resistor warming up). Either way, where there’s resistance and current, there’s heat.