How can you tell whether a medium has low or high index of refraction?

When these two media are compared, then, it is evident that rarer medium has lower refracted index as compared to denser medium. Denser media like glass and water have higher refractive index whereas rarer medium like air and vacuum have lower refractive index. Due to this, the light will bend towards the normal when it travels from rarer to denser medium. On the other hand, light will bend away from normal when it travels from denser to a rarer medium.

Whenever a light ray travels from a rarer medium to a denser medium through a spherical surface, relationship between object distance (u), image distance (v), radius of curvature (R) and refractive index ( $n_1$ and $n_2$ ) is given by refraction formula for spherical surfaces as follows.

$$\frac{n_2}{v}-\frac{n_1}{u}=\frac{n_2-n_1}{R}$$

• $n_1$ is the refractive index of medium that contains the object (on the left side)
• $n_2$ is refractive index of medium that will contain the image (on the right side)

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