Oil is optically denser than water. When sound/light goes from optically denser medium to optically rarer medium, their velocity increase and they moves away for normal.

Appropriate Answer:

The sound wave speeds up and bends

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As, In optics we learnt that light undergoes refraction when travels from medium of different densities. Similarly, Sound also follows the law of refraction.

• It is due to the change of speed of water in different mediums, This makes it speed up or down depending upon the medium and their densities.

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