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Question
Explain reflection at the boundary of a rarer medium.
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Solution
- Consider a wave travelling in a solid medium striking on the interface between the solid and the air. The compression exerts a force F on the surface of the rarer medium.
- As a rarer medium has smaller resistance for any deformation, the surface of separation is pushed backward.
- As the particles of the rarer medium are free to move, a rarefaction is produced at the interface. Thus, compression is reflected as rarefaction and a rarefaction travels from right to left.

Reflection of sound at a rarer medium
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