different material (for example, glass is denser than air) or a material could be considered rarer in comparison to another (for example, water is rarer than diamond).
• A rare medium is easier for light to pass through. • A dense medium is more dense than the rare medium and harder for light to pass through.
a Vacuum
b Water
c Diamond FIG. 14.2 Objects can appear distorted due to the medium light travels through
Experimentally it is found that the direction in which the light turns depends on the path the light takes.
• As light travels from a rarer to denser medium, the ray refracts towards the normal (i1 and r1).
• As light travels from a denser to a rarer medium, the ray refracts away from the normal (i2 and r2).
The ray will always travel along the same path, even if it is reversed. Terms used in refraction
As with reflection, it is important to understand the terms required to describe a ray diagram involving refraction.
i1 rare medium
r1 i2
dense medium
r2
rare medium
FIG. 14.3 Refraction through rare and dense media
• Incident ray: the light ray coming into the medium • Refracted ray: the light ray leaving the medium • Normal: the perpendicular line drawn at the point of incidence of light • Angle of incidence, i: the angle between the incident ray and the normal • Angle of refraction, r: the angle between the refracted ray and the normal
