towards an analysis of errors made by university students ... - DSpace

y.E.N.
DA C. ANDRADE)
(Part one)
Now, before the quantum theory was put
forward,
there was no notion of natural units of radiant energy: it was
believed that we could have any amount of energy, as small
as
we pleased, radiated by a hot body or a luminous atom.
It could
however, be shown mathematically that, if this were true, we
should expect a hot body to radiate nearly all its energy in
the violet and ultra-violet end of the spectrum, which we know
to be against the facts of
observation.
The problem was solved
in the first year of the
-present century, when Planck showed that, to get the right
result, it was necessary to make a revolutionary
hypothesis:
to suppose that radiant energy was sent out in packets, as it
were - in units or atoms of energy, just as matter existed
in
atomic units. We cannot have less than an atom of lead,
say;
any minute piece of lead must consist of a whole number of
atoms. We cannot have an electric charge of less than an
electron.
In the same way, we cannot have less than z unit - or
quantum,
as it is called - of radiant energy, and any body that sends
out
or absorbs radiation must deal with one quantum or a whole number
of
quanta.
The little parcel of light of one particular
frequency in which radiant energy is delivered is sometimes
called a 'light dart', a very expressive term, but it is more
generally known as a photon. The photon is simply a quantum of
radiant energy, the only object of sometimes using the new
term