sound wall to the focal line after fail through a convex condensing & a convex variable vehicle sound to refract and lowers to magnify distant northern ->  a convex lens will cause the light to refract when the light passes through the convex lens  a convex lens will cause the light to refract when the light passes through the convex lens & bird is when sound observation -> a convex lens will cause the light to bend when the light passes through the lens