🔌Voltage, Current & Resistance

Voltage is the electromotive force that pushes electrons through a circuit — the electrical "pressure." Measured in Volts (V). Think of voltage as the height of a water tower: higher = more pressure. A 9V battery has 6× the "push" of a 1.5V AA cell. Voltage is always measured between two points — it's a potential difference, not an absolute value.

Resistance opposes current flow by converting electrical energy into heat. Measured in Ohms (Ω). Resistance depends on: material (ρ, resistivity), length (R ∝ L), cross-sectional area (R ∝ 1/A), and temperature (most metals: R increases with T). Superconductors have exactly R = 0 below their critical temperature.

Most through-hole resistors use 4 or 5 color bands. 4-band: Band 1 (1st digit), Band 2 (2nd digit), Band 3 (multiplier), Band 4 (tolerance). 5-band: three digits + multiplier + tolerance. Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Grey=8, White=9. Gold multiplier =×0.1, Silver =×0.01. Gold tolerance =±5%, Silver =±10%, Brown =±1%.