ELECTRIC CURRENT
Picture a piece of metal wire. Within the metal, electrons are zooming around at
speeds of about a million m/s in random directions, colliding with other electrons
and positive ions in the lattice. This is charge in motion, but it isn’t a net movement
of charge because the electrons move randomly. If there’s no net motion of charge,
there’s no current. However, if we were to create a potential difference between
the ends of the wire, meaning if we set up an electric field
the electrons would experience an electric force, and they would start to drift
through the wire. This is current. Although the electric field would travel through
the wire at nearly the speed of light, the electrons themselves would still have to
make their way through a crowd of atoms and other free electrons, so their drift
speed, vd, would be relatively slow: about a millimeter per second.
Don’t Get Swept Away
Earlier, we described the
capacitor as the dam of a
river. Extending on that,
consider the similarity