Inductor calculator
Inductive reactance is 2πfL. A 10 mH inductor at 1 kHz presents 62.8 ohms, rising in proportion to frequency. With a 1 µF capacitor it resonates at 1,592 Hz, and carrying one amp it stores 5 mJ.
How to use an inductor calculator
Inductors are the mirror of capacitors and the intuition follows from that. A capacitor opposes changes in voltage and passes high frequencies; an inductor opposes changes in current and blocks them. Reactance rises with frequency rather than falling, which is why an inductor makes a good series filter against switching noise and a poor one against mains hum. The stored-energy figure is the one that bites in switching supplies: interrupting an inductor carrying current forces that energy somewhere, and if there is no flyback path it appears as a voltage spike large enough to destroy whatever switched it.
Questions
XL = 2πfL, the AC opposition an inductor presents. It rises in proportion to frequency, unlike capacitive reactance which falls.
f = 1 ÷ (2π√(LC)). At that frequency the inductive and capacitive reactances cancel.
Half L times current squared. A 10 mH inductor at one amp holds 5 millijoules.
Because interrupting inductor current forces the stored energy out as a voltage spike. The diode gives it a path instead of your transistor.
L divided by R: the time for current to reach 63.2% of its final value, the inductive counterpart to RC.