Refraction through a glass slab
Ray bends towards normal in denser medium; emergent ray parallel to incident.
Step 1 — Study the figure
Cover the label key on the image, name each numbered part, then check the explanations below.
Step 2 — Diagram details for students
What this diagram shows
A ray through a glass slab bends at both faces but emerges parallel to the incident ray with a lateral shift. Light bends toward the normal when entering denser glass and away when exiting to air. Lateral shift depends on thickness and refractive index.
Numbered parts — mark & remember
Match each number on the figure with the meaning below. Say the function aloud once.
1 Incident ray
The incident ray approaches the first face of the slab in air. Draw a normal at the point of incidence. Angle of incidence is measured from this normal.
2 Refracted ray
Inside glass, the ray bends toward the normal because glass is optically denser. Speed of light is less in glass than in air. Show the bent segment clearly inside the rectangle.
3 Emergent ray
At the second face, light bends away from the normal into air. The emergent ray is parallel to the original incident ray for a rectangular slab. Parallel emergence is the key qualitative result.
4 Lateral shift
Although parallel, the emergent ray is sideways displaced. This displacement is the lateral shift. Thicker slabs and higher refractive index generally increase the shift.
How to read this figure
- Toward normal into denser medium; away from normal into rarer medium.
- Emergent || incident for rectangular slab.
- Mark normals on both faces.
Redraw for board marks
- Draw rectangular slab and two normals.
- Draw incident, refracted, and emergent rays.
- Show lateral shift with a small dimension mark.
Board answer tip: Draw slab refraction with normals and write two bending rules plus lateral shift definition.
Exam tips — don’t lose marks
- Do not say the final ray is permanently bent off-parallel after a slab.
- Define refractive index as ratio of speeds if asked.
- Optical density relates to refractive index, not mass density alone.