Chapter 17 Reflection and Refraction

Objectives 17.1 Explain the law of reflection 17.1 Distinguish between diffuse and specular reflection 17.1 Calculate the index of refraction in a medium

Objectives 17.2 Explain total internal reflection 17.2 Define the critical angle 17.2 Explain effects caused by the refraction of light in a medium with varying refractive indices 17.2 Explain dispersion of light in terms of the index of refraction

Reflection Specular: Mirror Diffuse: Everything else

What is Smooth? Are the molecular gaps smaller than the wavelength? Than specular reflection – Basketball is larger than gaps, so specular reflection occurs – Metals: Due to sea of electrons, form sort of a flatness (like flowing water) Are the molecular gaps larger than the wavelength? Than diffuse reflection – Most objects tend to have much larger gaps than 400 – 700 nm

In the House Application Mirrors are coated with Silver or Aluminum Silver is better (99 – 92), not every color equal Two reflections, one from glass, one from back Silver reflects 99 RG and 97 B Aluminum 92 RG and 90 B

Refraction

Snells Law How much refraction? Depends on speed of light through material n is speed of light where 1 is true speed Larger than 1 means slowed down (2 means half as fast

What is the index of Refraction If a light from a vacuum runs into water at 30 degrees, what is the angle of the light traveling in the water. N value of 1 for vacuum, 1.33 for water N values Vacuum 1.00 Air Water 1.33 Ethanol 1.36 Crown Glass 1.52 Quartz 1.61 Diamond 2.42

Total Internal Reflection When all light reflects due to a large angle (critical angle) – Looking into distance water = large angle = critical angle = total reflection

Total Internal Reflection Optic Fibers use this principal

Mirages Refraction of light through air (different densities)

Sunrise and Sunset Sun actually not where it appears to be

Going Fishing