Question Detail

The wave equation is y = 2 cos(20t - 0.008x + 0.35) (assuming 2δ is a misprint). The phase is φ = 20t - 0.008x + 0.35. The phase difference between two points separated by Δx is Δφ = 0.008 Δx. Δx = 0.5 m = 50 cm. Δφ = 0.008 × 50 = 0.4 rad. The options are in terms of δ. If δ = π, then 0.4 rad is 0.4π, not an option. The coefficient is 0.008 rad/cm. Δx = 50 cm. Δφ = 0.4 rad. If we express in terms of π, Δφ = 0.4π/π = 0.4π? The options are 0.2δ, 0.4δ, 0.6δ, 0.8δ. If δ = π, then 0.4 rad = 0.127δ. Not matching. There might be a misprint. If the phase is 20t - 0.08x + 0.35, then Δφ = 0.08 × 50 = 4 rad. Still not matching.