Magnetic field, alternated current and EMF

If I apply an alternated current to a solenoid and insert into it a smaller solenoid, I could measure the induced EMF (electromotive force) and study how it changes in relation to the frequency of signal generator.

If I increase the frequency, I think that the magnetic fiel increases and so also the EMF increases, isn't it?

If I insert a metallic cylinder between the two solenoids, the cyclinder "shields" the magnetic field.. but what about EMF? And what about EMF if the cylinder is made by iron?

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your question shows you dont have understanding of basic concepts including that of magnetic field and emf. so i would suggest you try to understand these first before trying to pose more detailed questions. –  guru Jul 1 '13 at 18:16
@guru I'd like to know where you can see that I haven't understood the basic concepts of magnetic field and emf. –  sunrise Jul 1 '13 at 19:13
"If I insert a metallic cylinder between the two solenoids, the cyclinder "shields" the magnetic field.. but what about EMF? And what about EMF if the cylinder is made by iron?" do you know how emf is connected to change of magnetic field, for eg.? if you did, would you feel the need to ask this question? –  guru Jul 2 '13 at 4:06

1 Answer

Your question is so confused that it's difficult to answer, so I'll just point out a few things.

• What you seem to be describing with a solenoid within a solenoid is a transformer. That would be a good keyword for more research.

• The magnetic field strength is linearly proportional to the current thru the driven solenoid. Changing the frequency doesn't change this. The instantaneous magnetic field strength depends on the instantaneous current, whether it had a different value recently or will have a different value in the near future or not.

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if I change the frequency, the impedence of the inductor changes and so the current changes too. You can see that the magnetic field changes. –  sunrise Jul 1 '13 at 19:02
@sunri: Read your own question more carefully. You specified driving the coil with a particular current. That means the current is what it is. Yes, the impedance of a inductor goes up with frequency, but that only means you will drive it with a higher voltage to achieve the same current. The magnetic field strength is always directly proportional to the current, regardless of what voltage it took to produce that current. –  Olin Lathrop Jul 1 '13 at 20:41