Kundt's Tube Acoustic Standing Wave & Dust Node Chamber
A challenging, hands-on discovery and STEM project designed for curious young minds aged 10 to 14.
Materials Needed
- • Clear rigid acrylic tube (approx. 1 meter long, 4–5 cm diameter) (1 tube)
- • Small 4-ohm or 8-ohm mini speaker (or portable phone speaker) (1 unit)
- • Audio Tone Generator app (smartphone or tablet) (1 unit)
- • Fine cork dust, lycopodium powder, or micro-beads (2 tablespoons)
- • Rubber stopper and metric ruler (1 set)
Pro Tips
- → Sprinkle a thin line of fine cork dust or lightweight powder along the bottom of an acrylic tube sealed at one end.
- → Place a small speaker at the open end playing a pure sine wave tone (e.g., 1000 Hz to 3000 Hz) from a free phone app.
- → At resonance frequencies, the sound waves bounce back and forth, tossing the dust into dancing mounds at velocity antinodes, leaving clean gaps at nodes.
Safety First
Keep audio volume at a moderate level; do not operate high-decibel tones near ears.
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Step-by-Step Instructions
Step 1
Scatter a thin, uniform line of fine cork dust or pulverized foam powder along the inside bottom of a 1-meter clear acrylic tube.
Step 2
Seal the far end of the tube with a solid rubber stopper and mount a small speaker facing directly into the open near end.
Step 3
Play a pure sine wave tone from a phone app, slowly adjusting frequency until the powder suddenly dances into sharp, stationary ridges.
Step 4
Measure the distance between adjacent nodal dust piles with a ruler to calculate the acoustic wavelength and speed of sound.