If you were near an explosion in space, which of the following would be true?
You could both see it and hear it.
You could neither see nor hear it.
You could not see it but you could hear it.
You could see it but not hear it.

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.