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.

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