When two pure tones with similar frequencies combine to produce beats, the
result is a train of wave packets. That is, the sinusoidal waves are partially
localized into packets. Suppose two sinusoidal waves of equal amplitude A,
traveling in the same direction, have wave numbers \(\kappa\) and \(\kappa+\Delta
\kappa\) and angular frequencies \(\omega\) and \(\omega+\Delta \omega\),
respectively. Let \(\Delta x\) be the length of a wave packet, that is, the
distance between two nodes of the envelope of the combined sine functions.
What is the value of the product \(\Delta x \Delta \kappa ?\)