Question 6
A cathode-ray oscilloscope (c.r.o.) is used to determine
the frequency of a sound wave.
The diagram shows the waveform on the screen.
The time-base setting is 5.0 ms / div.
What is the frequency of the sound wave?
A 57 Hz B 71 Hz C 114 Hz D 143 Hz
Reference: Past Exam Paper – June 2018 Paper 13 Q22
Solution:
Answer: B.
The time-base setting is
5.0 ms / div.
That is, 1 div represents
5.0 mV.
To have a correct
measurement, we need to find positions where the waves occupy a ‘whole’ number
of divisions.
2.5 waves occupy 7 divisions.
2.5 T - - > 7 divisions
2.5 T = 7 × 5.0
T = 7 × 5.0
/ 2.5
Period T = 14 ms = 14×10-3
s
Frequency = 1 / T = 1 / (14×10-3)
Frequency = 71 Hz
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