Biomedical Engineering Reference
In-Depth Information
1
Electric Charges and their
Properties
As far as we can tell, there are four fundamental types of interactions between physical
objects. There is the
weak nuclear interaction
that governs the decay of beta particles, and
the
strong nuclear interaction
that is responsible for binding together the particles in a
nucleus. The familiar
gravitational
interaction holds the Earth very firmly in its orbit round
the Sun, and finally we know that there is an
electromagnetic
interaction that is responsible
for binding atomic electrons to nuclei and for holding atoms together when they combine
to form molecules.
Of the four, the gravitational interaction is the only one we would normally come across
in our everyday world. This is because gravitational interactions between bodies always
add. The gravitational interaction between two atoms is negligible but when large numbers
of fundamental particles such as atoms are aggregated together, the gravitational interaction
becomes significant.
You may think it bizarre that there are four types of interaction, yet, conversely, you
might wonder why there should be just four. Why not one, three or five? Should there not
be a unifying theory to explain why there are four, and whether they are related?As I write,
there is no such unifying theory despite tremendous research activity.
1.1 Point Charges
In this chapter I am going to concentrate on electric charges and their properties, since
electrons and protons are fundamental building blocks for atoms and molecules.
It turns out that there are two types of electric charge in nature, which we might choose
to call type X and type Y (or Red and Blue for that matter, but X and Y will do for
