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When creating a coil for a Crystal Radio, why do I have to have insulated windings? Why does it matter if the individual turns touch each other?

When it "shorts out" in this context, what does that mean, as in where did the charge go?

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  • \$\begingroup\$ Use so-called magnet wire. It's enameled and available in many gauges. \$\endgroup\$
    – jonk
    Sep 19, 2018 at 23:05

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If you use insulated wire, the current is forced to go all the way around each loop, and this helps add to the magnetic field that is crucial for the operation of an inductor. More turns = more field and more inductance.

If you use bare wire, the current will take the least resistance path, which would be the shortest path from one end to the other, and there will be virtually no magnetic field at all.

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  • \$\begingroup\$ Dave, In this case, what would be the shortest path? That is where I am confused. I thought it would go around all the coils regardless. \$\endgroup\$
    – johnny
    Sep 20, 2018 at 14:49
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    \$\begingroup\$ Why would it do that if it can jump directly to the next coil? Going the long way around is much more resistance than the direct connection. It also represents an inductance, which also impedes the flow of current. \$\endgroup\$
    – Dave Tweed
    Sep 20, 2018 at 14:50
  • \$\begingroup\$ My edit did not help. \$\endgroup\$ Sep 20, 2018 at 15:22
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    \$\begingroup\$ @HarrySvensson: Evidently not :-( \$\endgroup\$
    – Dave Tweed
    Sep 20, 2018 at 15:28
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    \$\begingroup\$ @johnny: Imagine this: If each turn of the bare wire wound on the form touched its neighbors continuously along its length, it would be exactly equivalent to wrapping the form with a sheet of copper foil. You could also think of it as a short piece of copper tubing. There's nothing that would force current to make several trips around the circumference rather than following the direct path from one terminal to the other. \$\endgroup\$
    – Dave Tweed
    Sep 20, 2018 at 15:32
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Yes it matters if the wires are insulated.

Using regular insulated wire rather than enamel will result in a much larger coil.

If the individual turns touch each other then the current can flow along the length of the coil rather than going around all the loops. This will change the inductance of the coil so it won't tune to the frequencies you want.

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  • \$\begingroup\$ What about the other parts of the wire though? Say it took a straight path across the top of the coils (if that is what you mean), what's in the rest of the wire? Nothing, small charge, something else? \$\endgroup\$
    – johnny
    Sep 20, 2018 at 14:50
  • \$\begingroup\$ @johnny Nothing noticeable, for sure. \$\endgroup\$
    – user253751
    Sep 24, 2018 at 4:29
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If the individual turns are bare and touch each other, then you don't have a coil but just a piece of wire. The effective inductance would be very low.

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