# If I change the phase of a current running through a loop of wire, does the magnetic field produced by the loop change its phase by the same amount?

Running a current through a few loops of wire produces a magnetic field. If I change the magnitude and phase of the current, the magnetic field magnitude will scale linearly with the change in magnitude in the current, but will the phase of the field also change linearly with the current? I'm talking about a current with a normal sinusoidal waveform, but does the answer change for a broadband or other type of waveform?

In general, yes. The magnetic field is proportional to the instantaneous current, so if you change the current waveform then the magnetic field will change in the same way. Note that if there is a magnetic core inside the loop, then it is possible for the core to saturate, which will change things.

• So if the current phase shifts by 3 degrees, the H field will also shift by 3 degrees? Commented Sep 22, 2016 at 13:08
• H field is controlled by current phase
• E field is controlled by voltage phase

Phase can change polarity on harmonics due to signal

• e.g. triangle vs square wave both have (only) odd harmonics
• but triangle has all harmonics in phase (0)
• while square wave has harmonics with -90deg or negative phase.

Saturation is noted with 3rd or 5th harmonic current rises or L drops 10%

Sine drive with current distorted in core from saturation.