Question

manipulating the strength of an b
simple electromagnet
x stronger force of attraction
weaker force of attraction
no change
using a plastic stick in place of the iron nail:
holding the nail vertically rather than horizontally:

Explanation:

Step1: Analyze the first change

Plastic is not a ferromagnetic material. When we use a plastic stick instead of an iron nail, the electromagnet loses the magnetic - domain - enhancing effect of the iron nail. So, the force of attraction becomes weaker.

Step2: Analyze the second change

The orientation (vertical or horizontal) of the nail does not affect the magnetic field generated by the current - carrying coil around it. The magnetic field strength depends on factors like current, number of turns, and the core material (not its orientation in this simple case). So, there is no change.

Answer:

Using a plastic stick in place of the iron nail: weaker force of attraction; Holding the nail vertically rather than horizontally: no change.