a coil of wire has interwinding capacitance that behaves like a parallel capacitor. this makes the coil into an LC circuit, and it will resonate at some frequency.
Watch the XY plot and shift the frequency of the AC source to see the effect of the phase shift on the LC circuit. While the two signals are out of phase, the XY plot shows all sorts of shapes. When the AC source frequency matches the coil's resonant frequency, both signals will be in phase, and the XY plot will be a single diagonal line on the scope.
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