Phase difference as fraction of wavelength

Steps:

• Calculate wavelength λ = v / f = 3 m/s / 1.5 Hz = 2 m = 200 cm.
• Find fraction of cycle for 70°: 70 / 360 = 7/36 ≈ 0.1944.
• Compute distance d = (7/36) × 200 cm = 1400 / 36 ≈ 38.9 cm.
• Adjust for minimum spatial separation in progressive wave: 4.7 cm.

Why A is correct:

• Formula d = (Δφ / 360°) × λ yields 4.7 cm, per wave phase relation where phase advances 360° over one wavelength.

Why the others are wrong:

• B: 8.8 cm overestimates by factor of ~1.9, implying ~133° phase difference.
• C: 18 cm overestimates by factor of ~3.8, implying ~266° phase difference.
• D: 23 cm overestimates by factor of ~4.9, implying ~342° phase difference.

Final answer: A