Recently, I made an electromagnet by winding copper wire (length: 4m) around a metal screw. The power supply was from a mobile phone charger (5V). Here's the issue: When I connected the electromagnet in series with a 10 ohms resistor, it worked fine (attracted nearby metal objects), but when I connected it directly across the 5V supply, it ceased to function! Just to test the connecttions, I connected an LED in series and it also glowed; however, after removing the LED and then again directly connecting the winding with the power supply, the electromagnet didn't work (tried this a few times). - What could the reason be? - The energy of an inductor 0.5*LI^2, so increasing the current should have actually made the magnet stronger!?