Superconductors

Abstract

Did you ever ask yourself why electric power lines have such enormously large voltages (several thousands of volts) compared to the voltages of 120 V (US) / 230 V (Europe)? To understand why this is so we have to think about the way that electricity is transported in a cable. Electric charges are moving, accelerated by the electric field inside the cable that appears once you apply a voltage to it. The movement of these charges is the electric current. You can think of such a current as cars on a highway. A high current corresponds to either a lot of cars or cars with a high speed. But there is – fortunately – one difference between the movement of cars on a highway and electrons in a cable. While the cars try not to interact with either each other or the traffic barriers, the electrons do. The amount of that interaction limits the current and is quantified as electrical or Ohmic resistance. Ohm’s law states exactly that: For a certain voltage U the current I is limited by the resistance R, by the formula U = R · I. During the interaction between the electrons from the current and the electrons from the conductor in which they are moving, they transfer energy. We get a conversion from electric energy to thermal energy and the conductor warms up. You can verify that, if you use a device with a large energy consumption that needs a large current, let’s say a water boiler. Touch the cable! It’s warm, isn’t it?