Any wave. When moving from one medium to another intermediary one. Without a line perpendicular to the khetrawang intermediaries will have to either be the best message that causes refraction.
Any wave when passing from one medium to another medium one. Without perpendicular to the county line between media are turning. What are the biggest advantages is the cause of refraction.
Any wave when moving through from one medium to another medium as one. Not perpendicular to the line between the medium is refraction. Which item is a the biggest advantages is the cause of refraction.