Practice question

**Wave classification** depends on particle vibration relative to propagation. Longitudinal waves have particle oscillation parallel to propagation, creating compressions and rarefactions as in sound in air; transverse have perpendicular oscillation. Tuning fork generates longitudinal sound because air cannot sustain shear. For a progressive wave, phase difference Δ Φ = k Δ x , where k = (2π/λ) . If Δ x = λ , then Δ Φ = (2π/λ) × λ = 2π , meaning they are in phase. Using v = fλ and standing-wave condition fₙ = n v/(2L) or v/(4L) as applicable, calculation yields In phase, illustrating frequency-length-speed interdependence and quantization by boundaries.