3 · IGCSE Physics
Sound on an oscilloscope
A microphone feeds a sound wave into an oscilloscope. Change the pitch, loudness, time-base and Y-gain, then count squares to find the period and frequency yourself.
T = (divisions per cycle) × (time-base)
f = 1 / T
amplitude = (divisions) × (Y-gain)
f = 1 / T
amplitude = (divisions) × (Y-gain)
Try this
- Set 500 Hz and 0.5 ms/div. Count the divisions for one full cycle, multiply by the time-base to get T, then check that f = 1/T gives 500 Hz.
- Double the amplitude while keeping the frequency fixed. What changes on the screen, and what stays the same? Which property of the sound is louder, and which is unchanged?
- Press Mystery sound, then pick a time-base that shows one to three cycles. Measure T over several cycles for accuracy, work out f, and untick Hide values to check.
Common error: counting divisions but forgetting to multiply by the time-base and convert ms to s before using f = 1/T, which gives a frequency wrong by a factor of 1000.