Transcript Goal: To understand what Electric Fields are

Goal: To understand reflection
and refraction
Objectives:
1) To understand Reflection off of a simple
mirror
2) To learn about Scattering
3) To understand Refraction
4) To learn about Mirages
5) To explore Rainbows
6) To learn about Total Internal Reflection
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 (θr = θi), 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.
Plane mirrors
• These are the sort of mirrors you find in a
bathroom.
• They are straight and flat. (below from a
website)
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.
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).
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.
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
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?
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…)
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.