The property that causes a pencil to appear bent or broken when placed in a glass partially filled with water is called refraction. Refraction occurs when light waves pass through different mediums, such as air and water, at different speeds. When light enters a medium with a different optical density, such as water, it changes direction, causing the pencil to appear bent or broken. This phenomenon is caused by the bending of light rays as they pass from one medium to another.
