CRO measurement of frequency
Microphone into a CRO. Adjust the time-base until 2–3 cycles fill the screen. T = (divisions spanned by ONE cycle) × time-base setting, then f = 1/T. Count intervals honestly — traces usually show 2.5 cycles, and μs/ms time-base conversions are part of the question.
What this actually means
The CRO turns sound into a voltage-time graph. The only measurement you make is the period: count the divisions spanned by one complete cycle and multiply by the time-base setting. Then f = 1/T.
For accuracy, measure across several cycles and divide by the number of cycles, and choose a time-base that puts two to three cycles on screen, neither a squash nor a stretch.
Cycle counting is where marks die: a screen usually shows 2.5 cycles, not 2 or 3. And watch the time-base units; ms versus μs conversion errors are built into the question on purpose.
Miscounting cycles on screen (2.5, not 3) or fumbling the ms/μs time-base conversion.
Prove it — watch it be true
- Turn the time-base knob until 2–3 cycles sit on screen
- Place the cursors exactly one cycle apart and read T
- Compute f = 1/T and compare with the hidden true frequency — the % error is your honesty score