What a learner can do afterwards
- Predicts how resistance changes when a wire is stretched, doubled in length or swapped for a thicker one
- Calculates a resistivity from measurements of resistance, length and diameter, with the diameter squared handled correctly
- Compares two materials by resistivity and says which suits a heating element and which a connecting lead
1 · Read
One wire owns its drag; its stuff owns a deeper mark. The tie is R as rho L by A. Twice the run means twice the drag; twice the cut means half.
Stretch a wire to twice its run at same cut and drag doubles. Fold it back to half run with twin cut and drag drops to a fourth. Small shifts in width swing wide since cut grows with width squared.
Heat turns use high-mark blends such as nichrome, which turn flow into glow. Links use low-mark copper that wastes scant power. Big rho fits fires; small rho fits links.
To weigh stuff, log drag, run, and width, then work rho as R A by L. Gauge width with fine jaws and square with care. Long, thin, hot, or high-mark lines all lift drag.
Long, thin, hot, or high-mark lines all lift drag, and rho alone tells which stuff fits which post.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.