RI Prelims 2004 P2 Q4
(a) The figure below shows a loudspeaker cone. The dot represents an air particle.
(i) Describe the movement of the loudspeaker cone when the loudspeaker is producing sound of frequency 400 Hz.
(ii) Describe the movement of the air particle as the sound wave passes.
(iii) Draw a displacement-time graph to show how the displacement of the air particle changes during one cycle of the sound-wave. Write a suitable value on the time axis.
(b) Sound waves travel in air with a speed of 330 m/s. Calculate the wavelength of a sound wave of frequency 400 Hz.
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Answer:
(a)
(i) The cone will vibrate left to right and left again, 400 times in 1 second.
(ii) The air molecules will vibrate about a mean position, from left to right and then left again, 400 times in 1 second (longitudinal wave).
(iii)
(b) v = fλ
330 = 400 * λ
λ = 0.825 m
