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 1.0003• 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