 # What unit is used to measure reactance?

## What unit is used to measure reactance?

B. Ohm
C. Ampere
D. Siemens

This is a really easy question, when you understand what reactance is exactly.

Reactance is one part of what we call Impedance. The problem is that impedance is in mathematical terms, a complex number. That means there’s a “real” part, and an “imaginary” part. The purely resistive part of an impedance value is, as you’d expect, the resistance. It’s also the “real” part of the equation. This is the part that DC voltage and power are calculated from.

The “imaginary” part is the reactance. “Well if its imaginary why do we care?”

The term “imaginary” is an unfortunate term coined by mathematicians a long time ago and managed to stick. We could go down the rabbit hole of complex numbers, square roots of negative one, and all that, but I’ll spare you the gory details of that for the moment.

Reactance is a sort-of-kind of but-not-really corollary to resistance that only applies to components that “react” to AC current. So we get the term “reactance.” In a circuit that has both resistive and reactive elements, if we apply a DC current, we will observe that the AC-reactive components basically don’t do anything. i.e. Capacitors will act as “open circuits” and inductors will act as just another piece of wire.

Add an AC component to the current, however, and the output of the circuit changes. Those AC-reactive components start doing their job and “react” to that current. This combined resistive-reactive property is impedance.

And impedance is measured in ohms (Ω), as is resistance. So, the answer is B) ohms.

G5A09 (B)