Answer: Hello there!
Straightening the wire will "diffuse" the strength of the magnetic field.
changing the direction of the current will change the direction of the magnetic field.
adding more coils will increase the magnetic field because each coil can create a magnetic field of his own, and you can add them up.
Placing a metal bar within the coils the metal can be polarized by the electromagnetic field of the coil, wich will increment the magnetic field.
Stopping the current will stop the electromagnetic field generated by the coil.
so the answers are:
Adding more coils and placing a metal bar within the coils.
