  We present a simple experiment that allows us to demonstrate graphically that
the intensity of sound waves is proportional to the square of their amplitude,
a result that is theoretically analysed in any introductory wave course but
rarely demonstrated empirically. To achieve our goal, we use an audio signal
generator that, when connected to a loudspeaker, produces sine waves that can
be easily observed and measured using an oscilloscope. The measurements made
with these instruments allow us to create a plot of amplitude versus sound
intensity level, which verifies the mathematical relationship between amplitude
and intensity mentioned above. Among the experimental errors, the plot obtained
is in excellent agreement with what is theoretically expected.
