What is a possible distance between two points on the wave that have a phase difference of 60°?

Question 14

A sound wave has a speed of 330 m s^-1 and a frequency of 50 Hz.

What is a possible distance between two points on the wave that have a phase difference of 60°?

A 0.03 m                     B 1.1 m                       C 2.2 m                       D 6.6 m

Reference: Past Exam Paper – June 2015 Paper 12 Q25

Solution:

Answer: B.

Speed v = 330 m s^-1

Frequency f = 50 Hz

Speed v = fλ

Wavelength λ = v / f = 330 / 50

Wavelength λ = 6.6 m

A distance equal to the wavelength corresponds to a phase difference of 2π / 360°.

360° - - > 6.6 m

1° - - > 6.6 / 360

60° - - > (6.6/360) × 60 = 1.1 m