In a mad frenzy, you decide to build the world's most powerful electromagnet to wipe out everyone's cell phone SIM cards. While constructing the device, you use low resistance wiring, an iron-iridium core, multiple tight coils, and a high-voltage low-amperage battery. When you activate the device, it generates enough power to wipe out only your own cell phone. Which of these components had the greatest effect on the strength of your electromagnet?