Two wave sources are oscillating in phase. Each source produces a wave of wavelength λ. The two waves from the sources meet at point X with a phase difference of 90°.

Question 15

Two wave sources are oscillating in phase. Each source produces a wave of wavelength λ. The two waves from the sources meet at point X with a phase difference of 90°.

What is a possible difference in the distances from the two wave sources to point X?

A λ / 8                          B λ / 4                          C λ / 2                          D λ

Reference: Past Exam Paper – June 2017 Paper 12 Q29

Solution:

Answer: B.

The 2 sources are in phase.

A distance equal to the wavelength corresponds to a phase difference of 360° (that is they are in phase – or phase difference = 0°).

360° - - - > λ

1° - - - > λ / 360

90° - - - > (λ / 360) × 90 = λ / 4

 
So, a phase difference of 90° corresponds to a distance equal to λ / 4.