A wave of frequency 15 Hz travels at 24 m s-1 through a medium.

Question 10

A wave of frequency 15 Hz travels at 24 m s^-1 through a medium.

What is the phase difference between two points 2 m apart?

A There is no phase difference.

B They are out of phase by a quarter of a cycle.

C They are out of phase by half a cycle.

D They are out of phase by 0.8 of a cycle.

Reference: Past Exam Paper – June 2015 Paper 11 Q25

Solution:

Answer: B.

Frequency f = 15 Hz

Speed v = 24 m s^-1

v = fλ

Wavelength λ = v / f = 24 / 15 = 1.6 m

A distance equal to the wavelength corresponds to a phase difference of by one cycle.

1.6 m - - > 1 cycle

2.0 m - - > 2.0 / 1.6 = 1 ¼ cycle

 

A phase difference equal to a 1 ¼ cycle is the same as the phase difference by ¼ of a cycle.