Question

Angle between wave velocity and particle velocity of a longitudinal wave is

Answer 1

Suppose the longitudinal wave is traveling from the left to the right horizontally. The wave particles of the longitudinal wave then oscillates back and forth horizontally, i.e., toward the right away from the equilibrium position, then turn around and moves backward to the left.

When a particle is moving toward the right, the angle between the wave particle and the wave itself is zero. When the particles moving backward the left, the angle between the particle and wave is

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