Diagram A Shows a ray of light passing through glass. When light passes through glass, the light ray refracts, which means it bends towards the middle. Refraction or deflection is the bending of light as it passes from one transparent substance into another.
Light bends whenever it travels at an angle into a material with a different refractive index, which is caused by a change in momentum. When light passes from air through a solid with parallel sides, it emanates parallel to the path of the light ray that infiltrated it.