A glass tube lies horizontally and is sealed at one end, with a thin layer of dust resting on its underside inside the tube. A loudspeaker is positioned close to the open end of the tube and sends out sound. The sound frequency is changed, and at one particular frequency a stationary wave is produced within the tube, causing the dust to collect into small piles. The separation between four heaps of dust is $30\ \text{cm}$. The speed of sound in the tube is $330\ \text{m s}^{-1}$. What frequency is the sound from the loudspeaker?
- A$1650\ \text{Hz}$
- B$2200\ \text{Hz}$
- C$3300\ \text{Hz}$
- D$6600\ \text{Hz}$