The diagram shows the arrangement of particles in a progressive sound wave at one particular moment. The wave travels with speed $v$. $P$ and $Q$ are two positions in the wave separated by a distance $L$. Which expression gives the wave’s frequency?
- A$\frac{v}{2L}$
- B$\frac{v}{L}$
- C$\frac{2v}{L}$
- D$\frac{L}{v}$