Is Reactance the Magnitude of Impedance or Its Complex Part?

[JesseC]

My notes say reactance is the magnitude of impedance, so I assume it means this:

$$|Z| = \sqrt{X^2 + Y^2}$$

but this is contradicted by numerous internet sources I've read which say that it is the magnitude of the complex part of impedance $$|Y|$$ . Could someone clarify this?

I'm more inclined to trust the internet given my lecturer is an Astronomer :P

 

[cabraham]

My notes say reactance is the magnitude of impedance, so I assume it means this:

$$|Z| = \sqrt{X^2 + Y^2}$$

but this is contradicted by numerous internet sources I've read which say that it is the magnitude of the complex part of impedance $$|Y|$$ . Could someone clarify this?

I'm more inclined to trust the internet given my lecturer is an Astronomer :P

The following is the correct form. R is resistance, & X is reactance. BTW, "Y" is admittance, the reciprocal of impedance. Did I help?

$$|Z| = \sqrt{R^2 + X^2}$$

Claude

 

[JesseC]

Yeah sorry, I've used confusing notation such that Z being a complex number was of the form Z = X+Yj. So the real part X is resistance, and the imaginary part Y is reactance. Clearly modulus of Z is something else altogether, what would its use be?

I have another question while I'm here: Is the phase of a perfect inductor or capacitor always +π/2 or -π/2?

Given that (using your notation) phase is arctan(X/R) and for a capacitor or inductor R = 0, then ±π/2 = arctan(±∞). I never trust myself when it comes to things involving circuits.