A sound wave is produced by a loudspeaker cone, which creates pulses of pressure by moving back and forth between two points X and Y as shown in the diagram.
The distance between points X and Y is 5.0mm and the loudspeaker produces pulses of pressure every 0.2 milliseconds.
The following statements about the sound wave produced are made:
P It has a speed of 25m/s
Q It has an amplitude of 5.0mm
R It has a wavelength of 5.5mm
S It has a fundamental frequency of 5.0kHz
Which of these statements can be correctly deduced from the information given?

Answer:

27) G

P – Wrong
We can immediately eliminate P since speed of sound in air = 330m/s

Q – Wrong
Amplitude is the distance between 0 and maximum displacement. Here the amplitude would be half of the distance travelled by the wave, i.e. ½ x 5 = 2.5mm

R – Wrong
We first need to know the frequency of the sound wave to find the wavelength.
Frequency = 1 ÷ T = 1/(2 ÷ 1000) = 5000 Hz
Speed = Frequency x Wavelength
Wavelength = Speed ÷ Frequency = 330 ÷ 5000 = 0.066m = 66mm (hence 5.5mm is wrong)

S – Correct
Frequency = 1 ÷ T = 1/(2 ÷ 1000) = 5000 Hz = 5 kHz
Since only statement S is wrong, G is the correct answer.