When a wave encounters an opening in a barrier, what phenomenon occurs?

When a wave encounters an opening in a barrier, diffraction occurs. This phenomenon involves the bending and spreading of waves as they pass through the opening or around the edges of the barrier. It is most notable when the size of the opening is comparable to the wavelength of the wave.

As the wave moves through the opening, it disrupts the original straight-line propagation, leading to a change in direction and distribution of the wavefront. This can result in the wave spreading out into the region behind the barrier, creating a pattern of interference and varying intensity.

In contrast, reflection refers to the bouncing back of a wave when it hits a barrier, while refraction involves the change in direction of a wave as it passes from one medium to another with a different density. Compression relates to sound waves and their pressure variations, not specifically to the behavior of waves passing through openings. Thus, diffraction is the correct phenomenon associated with waves encountering openings.