Magnetic Field From Coiled Wires

[KrizG]

I'm just curious why solenoids used to create a magnetic field, such as those used in electric motors are typically coils of thin copper wires with a dielectric separating each turn of wire instead of using a single cylindrical shell made of solid copper. Wouldn't using a cylinder shell made entirely of copper be more effective? Because of the decreased length, there would be much less electric resistance, and I believe the magnetic field would remain the same if the current density flowing through it were the same.

 

[Matterwave]

In a solenoid, the current flows in circles, slowly spiraling towards the other side. How can you get that behavior if you used a cylinder? The current would just move straight through, and then you get a magnetic field that's not in the direction you want.