Following Reflected and Refracted Rays

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Following Reflected and Refracted Rays
ÎRay
1 is the incident ray
ÎRay
2 is the reflected ray
ÎRay
3 is refracted into
the lucite
ÎRay
4 is reflected in the
lucite
ÎRay
5 is refracted as it
enters the air from the
lucite
PHY2054: Chapter 22
8
Chapter 22 Quiz
ÎSnell’s
Law describes:
‹ (a)
Huygens’ construction
‹ (b) Magnification
‹ (c) Reflection
‹ (d) Refraction
PHY2054: Chapter 22
9
Chapter 22 Quiz
ÎFor
refracted light rays, the angle of refraction:
‹ (a)
is always equal to the incident angle
‹ (b) is always greater than the incident angle
‹ (c) is always less than the incident angle
‹ (d) is always equal to the critical angle
‹ (e) can be less than, greater than, or equal to angle of incidence
PHY2054: Chapter 22
10
Dispersion
ÎWhen
light travels from one medium to another:
‹ Speed
decreases
‹ Wavelength decreases
‹ Frequency constant
ÎRefractive
cn = c / n
λn = cn / f = ( c / n ) / f = λ / n
index is variable
on λ
‹ n decreases as λ increases
‹ Depends
n
PHY2054: Chapter 22
11
Dispersion
În
decreases as λ increases
red light (λ = 700 nm) ⇒ n is smaller (less bending)
‹ For blue light (λ = 400 nm) ⇒ n is bigger (more bending)
‹ Spreading (“dispersion”) of colors due to refraction
‹ For
PHY2054: Chapter 22
12
Rainbows Formed by Dispersion
ÎLight
is refracted by spherical water droplets
must be behind you (rainbow is circular, with sun on axis)
‹ Red light bent at a lesser angle
(top of rainbow)
‹ Violet light bent at a greater angle (bottom of rainbow)
‹ Sun
PHY2054: Chapter 22
13
Understanding Refraction in Wave Picture
ÎConsider
a row of soldiers slowing down in the mud
‹ Wave
fronts “turn” due to change of speed in the medium
‹ Analysis based on Huygens principle
‹ Closer analysis yields Snell’s law with cn = c / n
PHY2054: Chapter 22
14
Critical Angle
Îθ
< θc beam partly reflected & partly refracted at boundary
Îθ
> θc beam is entirely reflected at the boundary
‹ Total
internal reflection occurs only when n1 > n2
sin θc = n2 / n1
sin θ c = n2 / n1
90°
PHY2054: Chapter 22
15
Critical Angles (to vacuum)
Substance
sin θc = 1/ n
N
Critical angle
1
90.0°
Air
1.00029
88.6°
Ice
1.31
49.8°
Water
1.333
48.6°
Ethyl Alcohol
1.36
47.3°
Glycerine
1.473
42.8°
Crown glass
1.52
41.1°
Sodium chloride
1.54
40.5°
Quartz
1.544
40.4°
Heavy flint glass
1.65
37.3°
Tooth enamel
1.655
37.2°
Sapphire
1.77
34.4°
Heaviest flint glass
1.89
31.9°
Diamond
2.42
24.4°
Vacuum
PHY2054: Chapter 22
16
Intensity During Transition to Critical Angle
ÎTransition
is actually very smooth
ray is reflected and refracted
‹ As incident angle approaches critical angle, intensity of refracted
ray goes to zero and reflected ray takes all the intensity
‹ Incident
PHY2054: Chapter 22
17
Fiber Optics
ÎBased
on total internal reflection
‹ Fiber
has inner “core” of optically dense glass
‹ Outer “cladding” of less optically dense glass
ÎLight
rays passed through core to make shallow
reflections with surface ⇒ 100% reflection at each bounce
PHY2054: Chapter 22
18
Fiber Optic Construction
ÎTrick
is to make core absorb no light
‹ So
light can be transmitted over long distances
‹ Requires ultra-pure glass (no impurities, variations)
ÎMany
fibers can be carried in a bundle
PHY2054: Chapter 22
19
Construction of Fiber Optic Cable
Single mode fiber
PHY2054: Chapter 22
20
Medical applications
ÎVisual
ÎUses
scoping of internal organs, arteries, joints, etc.
bundles of fibers to form an image
PHY2054: Chapter 22
21
Fiber Optic Cables
PHY2054: Chapter 22
22
Communications Applications
ÎOptical
fibers can carry digital information
‹ Telephone,
ÎHigh
networks, Internet
frequency of light ⇒ high rate of information transfer
‹ “High
ÎSignals
‹ Not
bandwidth”, several Tb/s over single fiber
can travel ∼ 100 km before needing boost
susceptible to electrical noise
ÎReplacing
copper wires for long distance communication
PHY2054: Chapter 22
23
Chapter 22 Quiz
ÎTotal
internal reflection
‹ (a)
refers to light being reflected from a plane mirror
‹ (b) may occur when a fisherman looks at a fish in a lake
‹ (c) may occur when a fish looks at a fisherman on a lake
PHY2054: Chapter 22
24
National Lambda Rail Fiber Infrastructure
www.nlr.net/
Only NLR Backbone links shown
PHY2054: Chapter 22
25
Florida Lambda Rail (10 Florida Universities)
www.flrnet.org/
PHY2054: Chapter 22
26
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