All electrical laws
Self-induction law
Also known as the Inductor v–i law · v = L di/dt.
The voltage across an inductor is proportional to the rate of change of the current through it, the constant of proportionality being its inductance — Faraday's law applied to a coil's own flux linkage.
v = L × di/dt, E = ½LI²
- v
- voltage across the inductor (volts)
- L
- inductance (henries)
- di/dt
- rate of change of current (amperes per second)
- E
- energy stored in the magnetic field (joules)
In plain English: Current through a coil has inertia — it cannot jump. Try to change it fast and the coil answers with whatever voltage it takes to resist. Interrupt it instantly and di/dt goes enormous: that is the spike that kills transistors.
Where you'll meet it: Buck/boost converter design, why every relay and solenoid needs a flyback diode, why a stepper's current rise time caps its top speed, and why an inductor stores energy instead of burning it.
Calculators that use this law
Capacitive and Inductive Reactance CalculatorX_C = 1 / (2πfC)LC Resonance Calculatorf₀ = 1 / (2π√(LC))RLC Impedance CalculatorZ = √(R² + (X_L − X_C)²)Transformer Turns Ratio CalculatorN_p / N_s = V_p / V_s = I_s / I_pFaraday's Law EMF Calculatore = −N × (dΦ / dt)Capacitor and Inductor Stored Energy CalculatorE = ½ × C × V² (capacitor)
Components this law governs
Inductor / Coilv = L·di/dt is the defining equation — the coil resists current change and stores ½LI² in its field while doing so.Choke / Common-mode ChokeA choke is an inductor chosen for its opposition to fast changes — high di/dt noise sees a high voltage drop, DC sails through.Switching Regulator (Buck/Boost)v = L·di/dt is the converter: the inductor is charged from the input then dumped to the output, so the duty cycle sets the voltage ratio.Stepper Motorv = L·di/dt is the stepper's speed limit: at high step rates the current has no time to reach full value, so torque falls off a cliff.SMPS / Power SupplyEnergy is stored in the inductor each cycle and released to the output; duty cycle sets how much, and hence the regulated voltage.DC-DC Converter (buck/boost module)v = L·di/dt is the converter equation — a buck's output is Vin × duty cycle precisely because the inductor volt-seconds must balance.