The **wavenumber**
of a wave has a special significance in both classical and quantum physics.
Because waves are quantized (they can only occur in ``packets'' of
energy and momentum
)
we are often in the position of asking * what possible values*
* k * can have, and * counting* the number of allowed
* k * values.
From this procedure arises the notion of ``* k*-space'' and the
* density of states* in * k*-space, which may seem rather exotic
on the first encounter but with which every physicist ultimately
becomes intimately familiar.

The following arguments apply to * any* sort of wave
(or * wavefunction*) that is * confined to a finite region*
and constrained to have * nodes* at the * boundaries*.

- Counting Modes in 1 Dimension
- Counting Modes in 2 Dimensions
- Counting Modes in 3 Dimensions
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