Chapter 35, Problem 28P

Go Figure 35-40 shows I two isotropic point sources of light (S₁ and S₂) that emit in phase at wavelength 400 nm and the same amplitude. A detection point P is shown on an x axis that extends through source S₁ The phase difference ϕ between the light arriving at point P from the two sources is to be measured as P is moved along the x axis from x = 0 out to x = +∞. The results out to x_s= 10 × 10 7 m are given in Fig. 35-41. On the way out to + θ, what is the greatest value of x at which the light arriving at P from S₁ is exactly out of phase with the light arriving at P from S₂?

Figure 35-41.