In a station, two buses A and B are side by side motionless. You are in bus A looking at the passengers of bus B. You notice that one of the buses is in motion relative to the other. Which bus moved?

the answer is neither ball has a charge.

because if they were both positively charged, they will repel each other.

if they were positively and negatively charged, they will seek.

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.