Vol. IV — Electronics · Tool
A resistor and an inductor set how fast current rises or falls. Change R and L — τ updates as you type, with the familiar 63%, 95%, and 99% marks.
τ (tau) for an RL circuit is inductance over resistance: τ = L / R. After one time constant, current reaches about 63% of its final value; after three, about 95%; after five, about 99%. When you open the path, current falls by the same marks toward zero.
Bigger L stretches the curve; bigger R shortens it. Relay coils, motor windings, and series chokes all settle on this ratio. The secondary figure R / (2πL) is a rough corner-frequency scale for a simple RL high-pass — useful context, not a full filter design.
Pair this with RC time for the capacitor twin, check AC with Reactance, or pick resistors on Resistor codes.