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I have a question about AC magnetic field, wondering if you can help me understand this.

For a DC solenoid coil, We can say Magnetic field H=N*i/L (simplest form)

For an AC input, H=N*isin(wt)/L ; H(rms) = N*i/L (i is RMS value)

As long as the current i-rms is kept constant, the solenoid must produce the same magnetic

field at any frequency. But,in my measurements, even if I keep the current constant, the field

is still dropping as the frequency is increased (from 100 Hz to 10kHz).

I wonder why the field decreases..

I understand that apparent power increases because of the inductance, eddy current etc..

Does the field really reduce with frequency?

I wonder if there is any different formula to estimate the field at high frequency.

Thanks

Chitra