Current Bench

Live circuits you can poke: 40 lessons from Ohm's law to power supplies, motor drives, PCBs, RF and EMC, each with the physics, real-world numbers and a quick quiz, plus a sandbox to build your own. Wire color shows voltage, moving dots show current, glow shows heat.

Speed

voltage: − · 0 V · + charge moving (conventional: + to −) heat (power dissipated)

The three laws that run everything

Ohm: V = I · RVoltage across a part = current through it × its resistance. KVL: Σ V around any loop = 0Rises count +, drops count −. Every volt the source lifts, the parts drop. Voltage is like height. KCL: Σ I at a node = 0Currents in count +, currents out count −; they always sum to zero. Charge is never created or lost at a junction. Power: P = V · IWatts are joules per second, the heat or work in a part.

SI prefixes

Prefix	Symbol	Factor	Typical use
giga	G	10⁹	GHz RF, GΩ insulation
mega	M	10⁶	MΩ pull-ups, MHz clocks
kilo	k	10³	kΩ resistors, kHz audio
milli	m	10⁻³	mA, mH, mΩ traces
micro	µ	10⁻⁶	µF bulk caps, µA leakage
nano	n	10⁻⁹	nF, ns edges, nC gate charge
pico	p	10⁻¹²	pF parasitics, RF caps

Standard resistor values (E12)

10 · 12 · 15 · 18 · 22 · 27 · 33 · 39 · 47 · 56 · 68 · 82

Multiply by any power of ten (4.7 kΩ, 470 Ω, 47 kΩ). E12 parts are usually 5% or better tolerance; E24/E96 give finer steps for 1% parts.

Color-code bands: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9.