The four graphs show a progressive wave travelling along a stretched string. Graphs A and B illustrate how displacement $d$ changes with distance $x$ along the string at a single moment. Graphs C and D illustrate how displacement $d$ changes with time $t$ at one fixed value of $x$. The markings on the graphs are meant to indicate the wavelength $\lambda$, the period $T$ and the amplitude $a$ of the wave, but just one graph has been labelled correctly. Which graph is labelled correctly?
Physics 9702 · AS & A Level · Progressive waves