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?

15 centimeters

1 meter

5 meters

12.5 meters

The correct choice is

15 centimeters

The diffraction of the sound waves takes place when the wavelength of sound wave is comparable with the size of the object. Waves of wavelengths 1 meter, 5 meter, and 12.5 meters are comparable to the size of the doorway while the wavelength 15 centimeters is very small compared to the size of the doorway. hence the waves of wavelength 15 cm diffracts the least.

The answer is 15 centimeters. The waves with the smallest wavelengths (also highest frequency) have the least capacity to diffract around objects hence have a shadowing effect, behind the object, especially if the wavelength is small compared to the object. This is also the reason why high-frequency electromagnetic waves do not have a good reach in mountainous regions.