Light – Reflection and Refraction | Class 10 Science Notes

9.3.2 The Refractive Index

The refractive index quantifies how much light bends when passing from one medium to another. It is defined as the ratio of the sine of the angle of incidence to the sine of the angle of refraction (Snell's law). More fundamentally, it is the ratio of the speed of light in the first medium to that in the second medium. If light travels from medium 1 with speed v1 to medium 2 with speed v2, the refractive index n21 = v1/v2. When medium 1 is air or vacuum, the refractive index of medium 2 is called the absolute refractive index, n = c/v, where c is speed of light in air/vacuum and v is speed in the medium. Table 9.3 lists refractive indices of various media, showing that optical density relates to refractive index, not mass density. A medium with higher refractive index is optically denser. Light bends towards the normal when going from rarer to denser medium and away when going from denser to rarer. This explains everyday observations like the apparent raised position of objects in water.

📊 Diagram: Figure 9.11 showing refraction of light from medium 1 to medium 2 with angles of incidence and refraction.

🔗 Connection: Leads to the study of refraction by lenses and their image formation.

Table on page 16 (10×4)