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Light changes direction when it moves into a new medium (material) at an angle to the normal. This is called refraction. When light enters a transparent material from air, it turns towards the normal. When light leaves a transparent material and re–enters air it turns away from the normal. A ray that enters and leaves glass through parallel sides ends up in its original direction, but displaced to the side. Refraction can cause virtual images of objects to appear where light seems to be coming from.