This has been bugging me for a long time. Take this video for example.
I have always thought that electricity will take the shortest path. When the electromagnet's windings are uninsulated, it seems that the electricity would flow straight through the "mass of metal" created by the wire, not in the circular path needed for the electromagnet to work. I have also seen solenoids that work like this. How does this design work?
It is insulated. Have you ever noticed that sometimes solenoids are made from copper wire that seems distinctly non copper coloured?
This is called enamelled copper wire, and it available in a whole range of colours.
The insulation is just a very thin coating of polyurethane, polyamide or polyester. It shouldn't be confused with vitreous enamel, which is glass. The good thing about it is that you can easily remove the insulation by rubbing hot solder on the wire.
The wire is actually insulated. Most solenoids I've seen are wrapped with magnet wire or something similar. The wire is coated in a small amount of an insulating material. To create an electrical connection, you have to scrape off (or otherwise remove) this coating.
This insulation is thin and more windings are placed on the solenoid core than would fit with other insulations, it is also usually fairly indifferent to high temps. The goal is a high magnetic field in a small space. Often called magnet wire, transformer wire....
The thin insulation can also be verified by stripping it -- by using a small flame to burn it (I use a good-quality lighter, like BIC). Then, steel wool can be used to remove the remaining residue, making a very clean surface to accept your solder. This is in my experience the best way to remove the tough coating, especially for the thinnest magnet wire.
Just be careful to use the steel wool over a trash can, as the resulting dust creates much havoc with circuits and components like switches and potentiometers, and easily creates short-circuits with your circuit boards and fine-pitch chips.
Also be careful where the steel wool is kept, and don't let a 9-volt battery accidentally spark it off, which could cause a fire. I just keep it in a little container that has only that purpose (and is fastened in place).
