Use glass slabs which are rectangular block of transparent glass in optics experiments to study refraction.

When light passes through a glass slab, it bends toward the normal as it enters and away from the normal as it exits, due to the change in medium.

It helps demonstrate that the emergent ray is parallel to the incident ray, but shifted sideways, a concept called lateral displacement.

In physics labs, glass slabs are used to:

Verify the laws of refraction
Study the path of light rays through different media
Understand how refractive index affects light bending
They are essential in learning how light behaves at boundaries of two media and in developing ray diagrams involving transparent materials.