Goal: To understand reflection and refraction

1
Goal To understand reflection and refraction

• Objectives
• Reflection off of a simple mirror
• Scattering
• Refraction
• Mirages
• Rainbows
• Total Internal Reflection

2
When a photon meets a woman, err a surface

• A few things can happen, and often times you will
  get all of these in different amounts.
• 1) reflection the light in essence bounces off
  of the surface.
• In this case the angle which the light leaves is
  the same as it hits (?r ?i), as is the
  wavelength of light (in the perspective of the
  object it is hitting)
• The of light that gets reflected depends on the
  material it is hitting as well as the wavelength
  of light.

3
Plane mirrors

• These are the sort of mirrors you find in a
  bathroom.
• They are straight and flat. (below from a
  website)

4
Transmitted

• 2) Some light will be transmitted. That is it
  will pass through the material.
• This will also cause what is called refraction
  but more on that later.

5
Absorption

• 3) The material can absorb some of the energy.
• The percentage it absorbs at some wavelength is
  called the albedo.
• This can vary greatly with wavelength.
• A thin layer of water, for example, does not
  absorb much light in the optical.
• However, in the infrared it absorbs a LOT of
  energy.
• Thus water vapor is a greenhouse gas (and the
  most abundant greenhouse gas in our atmosphere).

6
Scattering

• 4) Scattering.
• This is similar to reflection.
• However, most surfaces are not smooth.
• So, when the light hits the surface, it is not
  hitting a flat surface.
• So, different light photons at slightly different
  positions can hit at a vastly different angle to
  the surface.
• Therefore, they will reflect at a wide range of
  angles.
• This is scattering.
• Also, if light hits an electron the electron can
  absorb the photon and reemit in a random
  direction thus scattering the light.

7
More on Refraction

• A surface is defined to be a point where the
  index of refraction changes.
• The most common form of this is when you have 2
  different types of materials such as air,
  glass, water, ect.
• For each the speed of light is different.
• When the light enters the material the speed
  changes but the rest of the wave which has not
  hit the surface is still going at the old pace.
• This causes an accordion affect (like cyclists
  hitting a hill and piling up).
• Also, the index of refraction depends on the
  wavelength of light more on this at the end of
  class

8
Now for something completely different

• But still the same.
• RAINBOWS!
• How are rainbows formed?
• (a lot of scribbling on the board is about to
  come)

9
Critical Angle

• The most the refraction angle can be is 90
  degrees (otherwise it would refract back into the
  substance, which does not make sense and is
  reflection)
• That means that if you go from high index of
  refraction to low index of refraction there is a
  point where the refraction angle is 90 degrees.
• This angle is called the Critical Angle.
• If your initial angle is BIGGER than this, then
  there is NO refraction (this is called total
  internal reflection)!
• Why would this be important?

10
Correction to book

• The textbook states at the end of chapter 28 that
  the telescope was invented in the 1500s. This
  not true it was definitely around earlier than
  that and may have been invented somewhere between
  1000-1200 AD (to be used as a spyglass).

11
Conclusion

• We learned about what light does when it hits a
  surface or travels into another medium.
• We now know how rainbows are created sorry for
  ruining rainbows forever for all of you.