Nodes and Antinodes
The wave drive is positioned at one end of the channel and its frequency slowly increased from zero. The fundamental resonance mode of vibration will occur at 0.8 Hz. Alternating high and low water levels will appear as corresponding broad and narrow splays of light on the viewing screen as indicated in Figure 16. The viewing screen is initially set about 1 foot above the water surface and raised or lowered for increased focus. The wave peaks and troughs correspond to the minimum and maximum density phases of acoustic resonance and are associated with its standing wave nodes.
As the wave drive is slowly moved along the channel length, two other positions of notable resonance behavior are found: one at midpoint, which is its antinode position, and the other being the far end where the initial response is repeated. The midpoint response of the relatively still water shows the antiresonant consequence of stimulating a vibrating system at its nodal position, i.e., analogous to harmonic absence due to pluck position on the string. Resonant and antiresonant characteristics of each successive harmonic vibration mode can be generated and observed through the sixteenth harmonic.
The antinode and resonance stimulation location of any harmonic (n = 1, 2, 3, . . . ) lies along the channel length (L) at a distance (lm) from either of its ends.
The node and antiresonant stimulation position of any harmonic (n) lies along the channel a distance (lm) from either end given by
These antinode and node locations correspond to those identified as “nodes and loops” by Strutt [Lord Rayleigh] (1945) in his discussion of the Kundt tube and also that covering harmonic absence and pluck position of a string.
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