How is the physical
change in the robot reversible,
and how can you tell that the
change follows the law of
conservation of mass?
need the answer ASAP

heats surface water up

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.