Sound waves generated in a classroom must diffract through an open doorway in order to propagate into the hallway.
Explanation;
Sound waves are a type of mechanical waves that requires a material medium for transmission, they are longitudinal wave with all the properties of other waves.
Diffraction is one of the property of waves that involves a change in direction of waves as they pass through an opening or around a barrier in their path. Sound wave diffract around corners or through the door openings, allowing people to hear others speaking to us from rooms that are adjacent.
