Q.Define inductive reactance $X_L$. Write its formula and SI unit, and explain how it varies with the frequency of the AC supply.

Definition. Inductive reactance is the constant $X_L$ appearing in the Ohm's-law-shaped relation $i_0=v_0/X_L$ derived for a pure inductor (Example 6):

measured, like resistance, in ohms ($\Omega$).

Frequency dependence. Since $X_L$ is directly PROPORTIONAL to $\omega$ (and hence to $f$): at $f\to0$ (approaching steady DC), $X_L\to0$, so an inductor offers essentially no opposition to a slowly changing or steady current -- consistent with a plain wire (zero resistance, ideally) behaving as a short circuit for DC. At high frequency, $X_L$ grows without bound, so an inductor increasingly RESISTS (chokes off) rapidly alternating current. …

State the formula from the pure-inductor derivation, then examine its two limiti …

• Confusing reactance's frequency-DEPENDENCE with resistance, which does not vary with frequency at all. …