Question

The hypotenuse of the right triangle of a vector diagram for R and XC, is it the impedance?

Answer 1

`R` is the resistance, while `X_C` is the capacitance. If you want to think about it this way, both are essentially types of resistance.

Resistance is the limitation to charge mobility due to the material through which charges can travel. Capacitance is just the capacitor's ability to store charge before it needs to release that charge as current.

Impedance is like an "overall resistance".

I've seen Impedance written as `Z`. The expression from my Principles of Instrumental Analysis textbook (Skoog, Holler, Crouch) is:

`Z = sqrt(R^2 + X_C^2)`

So yes, the hypotenuse of the vector diagram of this would be the impedance, when the phase shift `phi` between resistance and capacitance is `90^o`, like in a purely-inductive alternative-current RC circuit.

You can read more about it here:
http://www.learnabout-electronics.org/ac_theory/ac_ccts_51.php

(If someone else has more to add, go ahead)