A good methood of developing 'the naive physicist's' consepts is by starting from the odd, almost ludicrous, question: Why are
atoms so small? To begin with, they are very
small indeed. Every little piece of matter handled in every life
contains an enormous number of them. Many methods have been devised in an attempt to bring this fact home to the audience, none of them more impressive than the one used by Lord Kelvin: Suppose that you could mark the
molecules in a glass of water, then pour the contents of the glass onto the os\cean and stir the latter thoroughly so as to distribute the marked molecules uniformly throughout the seven seas, if then you took a glass of water anywhere out of the ocean, you would find in it about a hundered of your marked molecules.
The
actual sizes of atoms lie between 1/5000 and 1/2000 of the wave
length of yellow light. The comparison is significant, because the wave length roughly indicates the dimensions of the smallest
grain still recognizable in the microscope. Thus it will be seen that such a grain still contains thousands of millions of atoms, a fact which makes the actual visualization of a single atom impossible, considering thecurrent optic and electronic technology available.
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