In an experiment designed to create a stationary sound wave in air, a fine powder is first spread uniformly along the full length of a horizontal glass tube that is closed at one end. A loudspeaker at the open end of the tube sends in a sound wave with a fixed wavelength. A stationary wave then develops, and the powder gathers into evenly spaced heaps, as shown. Which statement explains where the powder heaps form inside the tube?
- AThe piles are where the air molecules vibrate with maximum amplitude.
- BThe piles are where the air molecules vibrate with minimum amplitude.
- CThe piles are where the air molecules vibrate with the highest frequency.
- DThe piles are where the air molecules vibrate vertically.