An unknown noise is generated in a building. Sound waves move toward an open doorway. Waves of which wavelength would diffract the least through the doorway and spread into the room?

Diffraction is least when a wave’s wavelength is much smaller than the opening it passes through. The doorway is the same size for all four waves, so the shortest wavelength spreads the least. Of the choices, 15 centimeters is the shortest wavelength.

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