利用電磁鐵自製摩打

將鐵釘從吸管取出,對電磁鐵的磁力有何影響?

Iron is a ferromagnetic substance, it can "concentrate" the magnetic field, thus increase the field strength. Removing the iron nails would weaken the magnetic field.

以一些不銹鋼物料代替鐵釘,結果有何不同?

Stainless steel is not ferromagnetic. This would not increase the field strength.

如何使線圈的轉動速度加快??

Increase the voltage of the battery, or have more turns on the coil.

如果在通電期間,線圈因一些外在原因而停止轉動, 會產生甚麼結果???

There is large current flowing in the coil. Either the battery or the coil, or both, will be heated up, and may be burnt eventually.