What phenomenon explains why we see a straw appearing bent in a glass of water?

The bending of a straw when it is placed in a glass of water can be attributed to the phenomenon of refraction. Refraction occurs when light passes from one medium to another, such as from air into water, leading to a change in the speed and direction of the light rays.

When light travels through air and enters the water, it slows down due to the higher density of water compared to air. As a result, the pathway of the light changes direction at the interface between the two mediums. This bending of light causes the portion of the straw that is submerged in water to appear misaligned compared to the portion above the water's surface, creating the visual illusion that the straw is bent.

The other concepts listed—reflection, diffraction, and interference—do not account for this specific visual effect. Reflection involves light bouncing off a surface, diffraction relates to the bending of light waves around obstacles or the spreading of light waves, and interference is a pattern formed by overlapping waves. None of these phenomena encapsulate the reason behind the apparent bending of the straw in water, which is distinctly characterized by the behavior of light when it transitions between different media, highlighting the importance of refraction.