Chapter 17, Problem 109P

In Fig. 17-53, a point source S of sound waves lies near a reflecting wall AB. A sound detector D intercepts sound ray R₁, traveling directly from S. It also intercepts sound ray R₂ that reflects from the wall such that the angle of incidence θ_i is equal to the angle of reflection θ_r. Assume that the reflection of sound by the wall causes a phase shift of 0.500λ. If the distances are d₁ =2.50 m. d₂ = 20.0 m. and d₃ = 12.5 m. what are the (a) lowest and (b) second lowest frequency at which R₁, and R₂ are in phase at D?

Figure 17-53 Problem 109.