Iron At High Frequencies, Does hf low voltage interact with iron

Hello, i would like to ask if Low voltage and a frequency of about 0.5 megahertz will interact with iron, i have made a simple coil like teslas secondary and primary, when i put iron inside the coil my light bulb dimmed, but i have made another coil, it is in a toroidal shape air core coil, now when i put iron inside it at the same frequencies the Bulb brightened up very much,
what is the difference between a coil wound in a straight line and a toroidal coil wound around a short paper tube?? i have used low voltage high frequency in my tests. please help clarify this, im obviously learning electronics,
Thank you very much to everyone!
Sumer

Where is the light bulb??

Iron at 0.5MHz has very low permeability (~10??) and very high loss (tan delta > 1).

A properly constructed toroid has very little external field. I'm pretty sure you didn't make a toroid...

Do you have drawings or photographs?

Tim

hi thanks for the reply. here is my drawing, dont know whats happening, would like to understand but couldnt find any info about this on the net.

you will ask what is the frequency generator were used in here, i have used a Thurlby thandar Tg 210 ,

That kind of behaviour is perfectly normal for a coil where the winding pitch is greater than the diameter of the winding. Your winding is almost zero thickness, and the pitch is considerably larger. Because of this the magnetic field from each half turn of primary winding partially cancels out the magnetic field from the opposite half turn. As a result you get very little coupling to the secondary winding. When you insert a magnetic core, it distorts the field in such a way that there is some improvement in the primary to secondary coupling.

You can see the effect of the thin form and large pitch in this diagram which is a cross section normal to the axis of the toroid:



Primary is red and and secondary is blue. Note the alternating direction of current flow in the primary conductors. The segments of secondary which are on the inside are close to one primary segment on the outside and two primary segments on the inside which are slightly farther apart. For the segments of secondary on the outside of the coil, the exact opposite is the case.

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