10/25/2010 1 Total Internal Reflection, Dispersion, Polarization • section 26-8 Physics 1161: Lecture 18 Total Internal Reflection normal θ 2 θ 1 n 2 n 1 Recall Snell’s Law: n 1 sin(θ 1 )= n 2 sin(θ 2 ) (n 1 > n 2 ⇒θ 2 > θ 1 ) θ 1 = sin -1 (n 2 /n 1 ) then θ 2 = 90 θ c θ i θ r “critical angle” Can the person standing on the edge of the pool be prevented from seeing the light by total internal reflection? 1) Yes 2) No Preflight 18.1 10 58% 42% 8 Indices of Refraction What is the critical angle of a diamond-air boundary? 1 2 1 sin c n n θ − = Internal Reflection in Diamond
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phy1161 18 handout internal reflection dispersionux1.eiu.edu/~cblehman/phy1161/0lectures_sp11/phy1161_18... · 2010. 10. 25. · Dispersion prism White light Blue light gets deflected
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10/25/2010
1
Total Internal Reflection, Dispersion,
Polarization
• section 26-8
Physics 1161: Lecture 18Total Internal Reflection
normal
θ2
θ1
n2
n1
Recall Snell’s Law: n1 sin(θ1)= n2 sin(θ2)
(n1 > n2 ⇒ θ2 > θ1 )
θ1 = sin-1(n2/n1) then θ2 = 90
θc
θi
θr
“critical angle”
Can the person standing on the edge of the pool be prevented from seeing the light by
total internal reflection ?
1) Yes 2) No
Preflight 18.1
10
58% 42% 8
Indices of Refraction
What is the critical angle of a
diamond-air boundary?1 2
1
sinc
n
nθ − =
Internal Reflection in Diamond
10/25/2010
2
The diagrams show incident rays approaching a
boundary with a second medium. The relative indices
of refraction of the two media are indicated. In which
diagram will total internal reflection occur, providing
the angle of incidence exceeds the critical angle?
1 2 3 4
0% 0%0%0%
1. Diagram A
2. Diagram B
3. Diagram C
4. None of these
Fiber Optics
Dispersion
prism
White light
Blue light gets deflected
more
nblue > nred
The index of refraction n depends on color!
In glass: nblue = 1.53 nred = 1.52
23
Skier sees blue coming up from the
bottom (1), and red coming down from
the top (2) of the rainbow.
Rainbow: Preflight 18.5
Which is red?
Which is blue?
Blue light is deflected more!
Alexander’s Dark Band
• Sky is light inside primary
rainbow
• Dark between primary
and secondary bows
• Light beyond the
secondary rainbow
• Dark region between is
called Alexander’s Dark
Band
22o Halo
• A halo is a ring of light surrounding the sun or moon.
• Most halos appear as bright white rings but in some instances, the dispersion of light as it passes through ice crystals found in upper level cirrus clouds can cause a halo to have color.