Home / Topics / Waves & Sound
Kundt's tube
Advanced
Measures sound speed using dust patterns.
A glass tube containing fine powder, with a vibrating rod at one end. The powder collects at nodes, whose spacing λ/2 gives the sound speed.
Powder nodes 0.5 m apart at 340 Hz give λ = 1.0 m, so v = 340 m/s.
Used in classic labs.
In more detail
In Kundt's tube, a rod is clamped at its centre and vibrated, while cork dust in a glass tube forms heaps at the nodes of the standing wave. The distance between heaps gives the wavelength.
Real-world uses
- Physics labs measure the speed of sound in gases and solids with Kundt's tube.
- It demonstrates standing waves visually.
- Physics teachers use Kundt's tube to show standing sound waves through a pattern of dust or cork in a tube.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
How do I get the speed?
Multiply the measured wavelength by the frequency of the vibration.
Why does the dust gather at nodes?
Because the nodes have little motion, so the dust is not thrown away.
What does the dust show?
Dust collects at the nodes, where the air is still, so the spacing between the piles gives half a wavelength.
Related topics in Waves & Sound
Open organ pipe · Closed organ pipe · End correction · Resonance tube experiment · Sound as pressure waves · Pitch and frequency