So... we were measuring RLC circuit, and while we inserted core into solenoid, the amplitude on osciloscope decreased. It would imply, that the core is diamagnetic. But it is original core from PHYWE solenoid and I don´t see a reason, to create solenoid with diamagnetic core. I´ve heard, that FeII could be diamagnetic, so is it posible, that iron core can change to be diamagnetic? I´m going to measure density of the core next time, just to be sure, that it really is iron.
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$\begingroup$ Amplitude of what decreased? You can measure voltage, current, etc. with an oscilloscope. $\endgroup$– honeste_vivereCommented Nov 30, 2015 at 15:48
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$\begingroup$ Amplitude of current. $\endgroup$– PedroCommented Nov 30, 2015 at 16:05
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$\begingroup$ "It would imply, that the core is diamagnetic." Why do you think that? If it was static current, I would expect it to decrease after ferromagnetic core is inserted into the solenoid - the process extracts energy from the system at the expense of EM energy. $\endgroup$– Ján LalinskýCommented Nov 30, 2015 at 21:19
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$\begingroup$ Well... solenoid in RLC circuit is like mass in LHO. Higher L means bigger amplitude. And if you put para/feromagnetic core in solenoid, L increase... That´s what I was told. $\endgroup$– PedroCommented Dec 1, 2015 at 13:08
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Not completely clear from your description, but do you mean that you tuned your frequency to achieve a current resonance and then inserted the iron core?
Did you not consider that the resonant frequency is completely changed by the increased inductance, so you would then be far from resonance at the same frequency? Depending on the resistance in the circuit, this could diminish the current very significantly.
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$\begingroup$ We were observing it in sweep mode, so we could see resonance curve. Than we were measuring amplitude around resonance frequency for solenoid with and without core - here is graph postimg.org/image/b4m587ru7 $\endgroup$– PedroCommented Dec 1, 2015 at 9:01
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$\begingroup$ @Pedro Please post something here if you do find what the problem is. Surely if you change L by a factor $\mu_r$ for Fe, then the resonant frequency should be very different? $\endgroup$– ProfRobCommented Dec 1, 2015 at 13:16