Two points .

The figure shows two point sources $S_{1}$ and $S_{2}$ that emit sound of wavelength $\lambda = 2.00 m$ . The emissions are isotropic and in phase, and the separation between the sources is $d = 16.0 m.$ At any point P on the x axis, the wave from $S_{1}$ and the wave from $S_{2}$ interfere. When P is very far away $(x = \infty),$ what are the phase difference between the arriving waves from $S_{2}$ and $S_{2}$ .

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