How does refraction happen when a light ray passes through a glass box?

When a light ray passes from the air into the glass the velocity of light decreases (the light waves slow down). This causes the direction of the waves to change. A change that can be drawn by drawing the ‘normal’ (a dotted line) perpendicular to the surface of the glass. As the light wave slows down it bends towards the normal. Now the light waves pass through the glass block. And when the light waves pass back into the air their velocity increases. When waves speed up they bend away from the normal. And this change in the bend causes the object to appear to have shifted position. This process is refraction and can happen when any wave changes speed and passes from one medium to another.