I'm trying to understand how an inductor works in an RL circuit. When I use an air core inductor, my estimation is fairly accurate to the test circuit but as soon as I use an inductor with a core, the calculations don't match the real circuit. Here are both examples values
V = 24V AC and f = 50Hz for both examples.
Example 1 - air core inductor R = 17 ohms (coil's resistance) and L = 20mH Calculations for XL, Z, I, etc match the measured values. No problem here.
Example 2 - 20mH inductor with core (https://au.rs-online.com/mobile/p/leaded-inductors/1633404/) R = 20 ohms (external resistance added because coil didn't seem to have much DC resistance) L = 20mH Calculations don't match the measurements at all. Infact, the inductor behaves as if it's not even in the circuit. Hardly any voltage drop across it and the circuit current seems to be controlled by the resistor.
I know there is something here that I don't understand, can anyone please help me identify what I'm missing and explain it? Why are the calculations not working as expected in the second example.