A Planar Cross Section Through Two Spherical Waves Emanating from the Sources

Multiple Choice

A planar cross section through two spherical waves emanating from the sources S₁ and S₂ in the plane is shown in the figure. The black circles are one and two wavelengths from their respective sources. The lighter circles are one half and one and a half wavelengths distant from their respective sources. If the phase at S₁ and S₂ is zero at this instant, and the waves shown arriving at P₂ both arrive with amplitude A, the difference in phase angle at point P₂ (in radians) is

A) 0.
B) π/2.
C) π.
D) 3π/2.
E) 2π.