What effect is observed when a straw appears bent in a glass of water?

The observed effect of a straw appearing bent in a glass of water is due to wave refraction. Refraction occurs when light travels from one medium to another, in this case, air to water. As light passes from the air into the water, it slows down due to the change in density of the mediums, which causes the light to change direction. This bending of light results in the visual distortion of the straw, making it appear bent when viewed from the side of the glass.

The phenomenon is a straightforward example of how light behaves when crossing an interface between two different materials, specifically air (less dense) and water (more dense). Understanding refraction is essential in explaining many optical illusions and behaviors of light in different environments. This principle is also responsible for various applications in optics, such as lenses and corrective eyewear.