I will increase the frequency in the RL network, resistance (intensity) and coil!
The red amplitude in advance increases with frequency (inductance: L * 2 * pi * f)
We arrive at the phenomenon of internal resonance, observe please
Intensity (resistance voltage: blue) is lagging and lower than the coil voltage: red
Here we are in phase and intensity I has become zero! Internal resonance!
If I increase the frequency again, the blue re-increases but especially 'passes before'
The coil now behaves like a capacitor!
The impedance of the coil now decreases proportionally to the frequency!
How does the coil become a capacitor?
Deepened in EMC, the explanation: a coil consists of contiguous isolated turns
2 conductors (turns) separated by an insulator (varnish of turns) form a capacitor
At resonance, the capacitor between turns is preponderant to the inductance of the turns
This is why, in CEM, the theoretical formulas serve you without this practical knowledge
This is important, and we will see it with the capacitor!
Do not hesitate to see our EMC courses if you like it!