Announcements 10/26/12



Prayer
Exam 2 going on…3 people taken it so far
a.Expected time?
Slinkies: Please turn in and cross your name off
the sign-out list, if you haven’t yet
Overboard
From warmup

Extra time on?
a. (nothing mentioned by more than one student)

Other comments?
a. Why does it stop at homework 20? How do we
see our other scores?
From warmup

Huygen's principle as stated in the textbook
involves "wave fronts". What is a wave front?
a. they are the crests of the waves of light
b. A wave front is a bunch of points having the
same phase.
Law of reflection illustrated
Credit: next several slides from Dr. Durfee
Law of reflection illustrated
Law of reflection illustrated
Law of reflection illustrated
Law of reflection illustrated
Law of reflection illustrated
Snell’s Law illustrated
Snell’s Law illustrated
Snell’s Law illustrated
From warmup

What does Snell's law have to do with total
internal refraction?
a. (my answer) TIR happens when Snell’s
law predicts that a refracted beam is
impossible
Demo

Stokes computer demo: (5:00)
http://stokes.byu.edu/teaching_resources/refract_script_flash.html
Total Internal Reflection

TIR: the equation
Demos




Blackboard optics
TIR in water soluble oil
Laser captured in stream of water
Fiber Optics
Clicker question:

If you have a -0.3 dB change, the final
intensity is what fraction of the initial
intensity? (You’ll need your calculator.)
a. 78%
b. 83%
c. 88%
d. 93%
e. 98%
-0.3 dB  93.3%
-0.2 dB  95.5%
-0.1 dB  97.7%
Clicker question:

When we think of all the points on a wave
front as little sources of secondary waves in
order to calculate what the wave front will
look like after propagating some distance, we
are using the idea known as...
a. the Equivalence theorem
b. Huygen’s Principle
c. Fermat’s Principle
d. Newton’s first law of optics
e. the Wavelet theorem
Huygen’s Principle
Image credit: Wikipedia


Each wavefront serves as source of spherical waves
HW 26-5 (extra credit):
a. “Stare at the picture until you can visualize that the green lines
tangent to the circles connect matching wavefronts.”
b. Construct an accurate picture like this for a specific situation,
show graphically that it gives you Snell’s law
Huygen’s Principle, cont.
Image credit: Wikipedia
http://en.wikipedia.org/wiki/
Double-slit_experiment



A wave hits the two slits
Each slit (infinitely narrow) becomes source of spherical
waves
The waves from those two sources interfere with each
other
Spherical Waves
Credit: the next few slides are from Dr. Durfee
Huygen’s Construction of a Spherical Wave
Huygen’s Construction of a Plane Wave