Danger Through Electromagentism Just for fun, you decide to build a powerful hand-held electromagnet that can generate a field strength of 0.5 T. You realize that by using a solenoid with a ferromagnetic core, you can achieve the desired field using a current of only 0.20 amps in the solenoid. You wind a copper wire several hundred times around an iron core, to build a solenoid with a resistance of 30 ohms and selfinductance of 0.50 H. You hook up the solenoid in series with a suitable emf, along with a simple on/off toggle switch. When you flip the switch on, you realize that a 0.5 T magnet is MUCH too strong to handle safely, so you quickly switch it back off againâbut when you do, you receive a really nasty electrical shock from the switch. On the way back from the ER, you wonder what average voltage was generated across the switch, just after it was opened. A quick internet search tells you that a typical current requires about 250 microseconds to die off to zero, after a toggle switch is opened.