light travels along a straight line as it moves in one medium. But when it moves from one medium to another it bends. The phenomenon of bending of light as it moves from one medium to another is called refraction of light.When a ray of light is incident on the glass slab, the emergent ray coming out of the slab will be parallel to the incident ray. The perpendicular distance between the direction of incident ray and emergent ray called the lateral shift.
This note provides us an information about real and apparent depth, total internal reflection and the critical angleAn object placed in a denser medium, when viewed from rarer medium appears to be at a lesser depth than its real depth due to refraction of light .