This topic accounts for approximately 7% of your exam marks.
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Stable7%
Speed of sound calculations, echo timing and ultrasound uses are standard shorter questions.
What an oscilloscope shows
An oscilloscope is an instrument that draws a graph of a rapidly changing voltage against time
A microphone converts the longitudinal vibration of air into a varying voltage, so connecting a microphone to an oscilloscope lets you "see" a sound wave on the screen
The displayed trace looks like a transverse wave, even though the underlying sound is longitudinal, because the screen is plotting voltage (y) against time (x), not the back-and-forth motion of air particles
Reading the trace
The time base sets the x-axis: how many milliseconds (or microseconds) correspond to each horizontal division on the screen
The y-gain sets the y-axis: how many millivolts correspond to each vertical division
Two quantities are read directly off a frozen trace:
Amplitude: the vertical height of a peak measured from the centre line; a louder sound gives a taller trace
Period (T): the horizontal distance between two corresponding points on the wave (peak to peak is easiest); a higher-pitched sound gives a shorter horizontal gap
Once T is known, the frequency of the sound is f = 1 / T
A higher-frequency sound fits more wave cycles across the same width of screen