https://www.wired.com/story/the-loopy-secrets-of-how-charging-cables-work/ > What do you do when your phone needs to be charged? You take a cable, plug in the phone, and boom: It's charging. What if you want to connect an external monitor to your laptop? Yup, there's an HDMI cable for that. To plug your phone into speakers, you might use an auxiliary audio cable. > But here's a secret. Inside each of those cables are multiple wires. It doesn't matter if the cable is used for power or for data—there have to be at least two wires inside. That is because all electric circuits depend on loops. You can't make a loop with just one wire.