Question

how can you \see\ amplitude and frequency?
sound waves are invisible. however, you can use
a tool called an oscilloscope to \see\ sound waves.
an oscilloscope is a device that can produce graphs to
represent sound waves.

how an oscilloscope works
the figures on the next page show examples of oscil-
loscope graphs of sound waves. notice that these graphs
look like transverse waves instead of longitudinal waves.
it is easier to see the amplitude and frequency of the
sound wave when it is graphed as a transverse wave. the
crests of the transverse wave represent compressions.
the troughs represent rarefactions.

reading check

1. describe on an oscillo-

scope graph, what do the wave
crests represent? what do the
wave troughs represent?

Explanation:

The problem is about sound waves and oscilloscopes, which falls under Physics (a subfield of Natural Science). From the text, on an oscilloscope graph of a sound wave (graphed as transverse), wave crests represent compressions (of the longitudinal sound wave) and troughs represent rarefactions.

Answer:

On an oscilloscope graph (treating sound wave as transverse for visualization), wave crests represent compressions (of the longitudinal sound wave) and wave troughs represent rarefactions.