Optical Phenomenal Chapter 14 section 3

Optical
Phenomenal
Chapter 14 section 3
Objectives

Predict whether light will be refracted or
undergo total internal reflection.

Recognize atmospheric conditions that cause
refraction.

Explain dispersion and phenomena such as
rainbows in terms of the relationship between
the index of refraction and the wavelength.
Total Internal Reflection

Total internal reflection can occur when light
moves along a path from a medium with a
higher index of refraction to one with a lower
index of refraction.

At the critical angle, refracted light makes an
angle of 90º with the normal.

Above the critical angle, total internal
reflection occurs and light is completely
reflected within
Critical Angle
 Snell’s
angle.
law can be used to find the critical
nr
sinC 
ni
sine  critical angle  
for ni  nr
index of refraction of second medium
index of refraction of first medium
•Total internal reflection occurs only if
the index of refraction of the first
medium is greater than the index of
refraction of the second medium.
Example
 Find
the critical angle for a water-air
boundary if the index of refraction of
water is 1.333
Atmospheric Refraction








Refracted light can create a mirage.
What is a mirage?
A mirage is an optical effect of the atmosphere caused by
refraction when light passes from air with one density into air with a
different density and the object appears displaced from its true
position.
The mirage called an inferior mirage occurs when the image
appears below the true location of the observed object.
During a phenomenon called looming, objects sometimes appear
to be suspended above the horizon.
Looming is considered a superior mirage because the image is
seen above its true position.
A mirage that changes the apparent size of an object is called
towering.
A type of towering, called Fata Morgana, is frequently observed in
coastal areas as towering castles that appear out of thin air.
Mirages
A
mirage is produced
by the bending of light rays in the
atmosphere where there are large
temperature differences between the
ground
and the air.
Mirages
Dispersion
 Dispersion
is the process of separating
polychromatic light into its component
wavelengths.
 White
light passed through a prism
produces a visible spectrum through
dispersion.
Rainbows





Perhaps the most spectacular and best known
atmospheric optical phenomenon is the rainbow.
Sunlight and water droplets are necessary for the
formation of a rainbow.
Furthermore, the observer must be between the
Sun and rain.
When a rainbow forms, the water droplets act as
prisms and refraction disperses the sunlight into the
spectrum of colors, a process called dispersion.
The curved shape of the rainbow results because
the rainbow rays always travel toward the
observer at an angle between 40 and 42° from
the path of the sunlight.
Rainbows
Lens Aberration
 Chromatic
aberration is the focusing of
different colors of light at different
distances behind a lens.
 Chromatic
aberration occurs because
the index of refraction varies for different
wavelengths of light.
Lens aberration
Video
 Watch
a video
Go over lab
 Lets
go over lab
Homework
 Do
problems 1-4 pg .502
Closure
Today we learned about optical
phenomena
Next class we are going to have a lab