Kundt's Tube
Plate 086 Physics Poster
Plate 86 speaks for itself: “Sound sweeps dust into rulers.”
The Physics
A standing sound wave in a tube sweeps fine powder into heaps at its nodes. The heaps are half a wavelength apart, so measuring them with a known frequency gives the speed of sound.
v = 2 f d
- v: speed of sound, m s⁻¹
- f: frequency, Hz
- d: spacing between heaps (λ/2), m
The heaps are λ/2 apart, so v = 2fd. Air at 20 °C: v ≈ 343 m/s.
Sources
- A. Kundt, Ann. Phys. 203, 497 (1866).
On the poster
Plate 086, “Kundt's Tube”: the pixel-art plate with its slogan “Sound sweeps dust into rulers.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.
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Field notes
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