Question 20
A loudspeaker produces a sound wave of constant
frequency.
Outline how a cathode-ray oscilloscope (c.r.o.) may be
used to determine this frequency. [4]
Reference: Past Exam Paper – November 2010 Paper 23 Q3
Solution:
A microphone (or terminals of a loudspeaker) is connected to the Y-plates of the c.r.o.
The c.r.o. is adjusted to produce a steady wave
of 1 (or 2) cycles (or wavelengths) on screen {using the time-base setting}.
The length of a cycle (wavelength λ) is
measured and the time-base b is noted.
{Period T = length of cycle × time-base = λb
Frequency = 1 / T = 1 / λb }
frequency = 1 / λb
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