CHAPTER 2: REFRACTION OF LIGHT

Refraction is the bending of light as it passes from one transparent medium to another. It explains why a straw looks broken in water, why pools appear shallower than they are, and why the sky appears to have mirages. It is also the principle behind lenses, spectacles, cameras, and the optical fibers that power the internet. Master this, and you master how light shapes our perception of reality.

2.1 SNELL'S LAW

When light travels from one medium to another (e.g., from air to glass), its speed changes. This change in speed causes it to change direction—it refracts. The amount of bending depends on the optical density of the two media.

2.1.1 The Law of Refraction

Snell's Law is the mathematical relationship that governs refraction. It states that for a given pair of media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant. This constant is called the refractive index of the second medium with respect to the first.

n = sin i / sin r

Where:

• i = angle of incidence (the angle between the incident ray and the normal—an imaginary line perpendicular to the surface).
• r = angle of refraction (the angle between the refracted ray and the normal).
• n = refractive index of the second medium relative to the first.