13.6. Electron Volts#
All of these powers of 10 are really irritating. More importantly, they represent mistakes just waiting to happen. Not to fear! We have a very useful unit of energy that works very nicely for atomic physics, nuclear physics, and particle physics: the “electron-volt” aka, “eV.” Here’s how it works.
Suppose we have another capacitor that has a 1 V battery connected to it. What’s the energy that a single electron (or proton, for that matter) would acquire as it’s accelerated through that 1 Volt difference? By now we know that it would be: $\( U = qV = (1.6\times 10^{-19}\text{ C})( 1 \text{ J/C}) = 1.6 \times 10^{-19} \text{ J}\)$
Ah. Since the fundamental electric charge quantity figures into so many things, let’s keep it hanging around as a symbol and define the electron volt to be:
We’ll see how this becomes useful and we’ll try to think in “electron volts” when we deal in energies appropriate to elementary particles.