The wave equation $v = f\lambda$ is used in almost every wave paper. You must be able to rearrange it: $f = v/\lambda$, $\lambda = v/f$.

From a displacement–time graph: measure the time for one complete cycle → period $T$, then $f = 1/T$.

From a displacement–distance graph: measure the distance between two consecutive crests → wavelength $\lambda$.

Many ‘analyse’ questions give a graph and ask you to deduce the frequency or wavelength, then calculate speed using $v = f\lambda$.

A classic 3‑mark ‘describe’ question: “Describe how you could demonstrate the difference between transverse and longitudinal waves using a slinky spring.”

Model answer:

- Stretch the slinky on the floor.

- For transverse: flick one end side‑to‑side. The coils move perpendicular to the direction the pulse travels.

- For longitudinal: push and pull one end. The coils move parallel to the direction of travel, showing compressions and rarefactions.

Diagrams are always helpful.