Answer:
1) Use a stronger battery
Explanation:
I'm going to quote Northeastern University (I could try to type out an explanation but this will probably be more concise)
"Electromagnets are made of coils of wire with electricity passing through them. Moving charges create magnetic fields, so when the coils of wire in an electromagnet have an electric current passing through them, the coils behave like a magnet."
4) So, if the coils are creating a moving charge, and there are more coils, each coil will be "setting up" its own magnetic field. This means that less coils will make the electromagnet weaker
2) Because it is an electro<em>magnet, </em>a plastic nail is not going to produce the same effect. An electromagnet is picking up metal, and it is not picking up plastic. This is because plastic (a material with low permeability) does not have a magnetic field that is able to interact with a magnet.
[Permeability is a measure of how easily magnetic lines of force can pass through a material.]
3) There's not really a point that I can imagine of gluing the wire to the nail. Glue would put more distance between the nail and the magnet than nothing being there at all.
1) More voltage in a battery produces a larger current in the wire. This means that the strength of an electromagnet is affected by the voltage/strength of the battery. So, a stronger battery would make the electromagnet stronger, and a weaker battery would make the electromagnet weaker.
