Electronics sometimes break down: your smartphone stops working, the toaster starts smoking. Is that due to wear of the power cord? After all, electrons run through that, and where there’s walking there’s friction – or rather resistance, in this case. What’s up with that?
A relevant question, says Bas Vermulst, electronics expert at Eindhoven University of Technology. He first explains what electricity actually is. Current is the movement of electrons: elementary particles with a negative charge. They are located around the nucleus of an atom, but can also jump from one atom to another. “They are actually parcels of cargo,” says Vermulst. “On a small scale they have quantum mechanical properties, for example that they are both a wave and a particle at the same time. On a larger scale, they behave like a continuous stream, similar to water molecules flowing together through a garden hose. In this case a flow of charge.”
thermal effects
Individual electrons move relatively slowly through a copper wire: at about 20 micrometers per second, or 7 centimeters per hour. “An electron takes many hours from the switch to the lamp,” says Vermulst. “But if an electron enters a wire at one end, another electron almost immediately exits at the other end. For example, the load moves at about 180,000 kilometers per second.”
While hopping between the atoms, the electrons are hindered. “Just like a river: it doesn’t flow faster and faster downhill,” says Vermulst. “The electrons have to work their way through the atomic lattice and experience thermal effects there.” At temperatures above absolute zero (-273°C), all particles vibrate in the grid. This results in collisions, causing the electrons to lose energy. “Something special happens only close to absolute zero: the resistance is then suddenly nil. That’s called superconductivity.”
In strongly cooled machines, superconductivity is responsible for the super strong magnetic fields of an MRI scanner or a particle accelerator, among other things. But that cooling is not possible in your smartphone or laptop. As a result, in consumer electronics there is always resistance and thermal effects occur. “They can eventually cause defects,” emphasizes Vermulst. “Such as the insulating sheath may become brittle or melt, or the wire itself may break due to constant expansion and contraction. We see the latter in the minuscule internal wiring of transistors and chips.”
Melting high voltage wires
Electric wires therefore do not wear out, says Vermulst. There is one exception: if the current becomes too large, it can generate so much heat that the wire melts. That is what recently happened in Flevoland: melting high-voltage wires fell on the overhead lines, so that trains could not run there for months. A smoking toaster has another problem: dust or breadcrumbs clinging to the wires.
Is there anything that can be done about the ‘ordinary’ thermal effects in electronics? Not as a consumer, Vermulst replies. “It’s mainly in the design. It is fine to take this into account, but costs often play a role. As a consumer you can only take good care of your batteries. For example, don’t leave your phone or the battery of your e-bike on the charger all night.” It is best if the charge of a battery remains between 20 and 80 percent, he advises: “For example, put a timer on the charger. Then the battery only loses a few percent of capacity annually, instead of 20 percent.”