16.2 Refraction

• The changing of a light ray’s direction (loosely called bending) when it passes a boundary between materials of different composition, or between layers in single material where there are changes in temperature and density, is called refraction. Refraction is responsible for a tremendous range of optical phenomena, from the action of lenses to voice transmission through optical fibers.
• varies. We define the index of refraction, n, of a material to be n = c/v where v is the observed speed of light in the material.
• The exact mathematical relationship is the law of refraction, or Snell’s law
• The incoming ray is called the incident ray and the outgoing ray is called the refracted ray. The associated angles are called the angle of incidence and the angle of refraction.
• The critical angle, 𝜃cθc, for a combination of two materials is defined to be the incident angle, 𝜃1θ1, which produces an angle of refraction of 90°.
• That is, 𝜃cθc is the incident angle for which 𝜃2θ2 = 90°. If the incident angle, 𝜃1θ1, is greater than the critical angle. Then all the light is reflected back into medium 1, a condition called total internal reflection.
• Such an object is called a corner reflector because the light bounces from its inside corner.