A tuning fork producing sound of frequency f f\,f is held above a vertical tube filled with water. A tap at the bottom of the tube is opened to allow the water to drain out slowly, creating an air column of increasing length.
A student hears a maximum in loudness (resonance) when the length of the air column reaches d1d_1d1. As the water level continues to fall, the next resonance is heard when the length of the air column is d2d_2d2.
Which expression gives the speed of sound v v\,v in the air column?
f(d2−d1)f(d_2 - d_1)f(d2−d1)
2f(d2−d1)2f(d_2 - d_1)2f(d2−d1)
4fd14f d_14fd1
f2(d2−d1)\frac{f}{2}(d_2 - d_1)2f(d2−d1)