View
220
Download
1
Category
Preview:
Citation preview
Reflection & Refractionof
Electromagnetic Radiation
ByEmin Menachekanian, PhD
What Is Light?
Wave Particle
ɤ
Electromagnetic Spectrum
The Speed of Light Is Finite, But Fast!
Consider the round-trip distance from here to UCLA and back: 30 mi ≈ 60 km
How much time is involved in the blink of an eye?
≈ 0.3 seconds!In that time, light would have made
an astonishing 1500 round trips!!
The Speed of Light Is Finite, But Fast!
Voyager 1, launched in 1977, took about 30 years to reach the edge of our solar system.
Light would take about 12 hours to do the same thing!!
Understanding How Light Reflects & Transmits
Use:Fermat’s Principle of Least Time
Pierre de Fermat
Fermat’s Principle of Least Time
Light will always take the path from one point to another that minimizes the
time of its journey.
In Empty Space:
What About for Reflecting from a Mirror?
Mirror
Mirror Image
What’s the Correct Reflection?
Mirror
A
B
Equidistant to Mirror
B’
This path not only minimizes the distance, but it also minimizes the time!
Because speed of incident ray is the same as the speed of reflected ray.
Law of Reflection
Mirror
A
BNormal to
Mirror
θi θr
θi = θr
Why Does He Look Like This?
Simple Example
Mirror
Simple Example
Mirror
Simple Example
Mirror
Transmission of Light
It takes time for the light to be re-emitted when captured → Slows down!
Speed of light in medium Speed of light in empty space
Index of Refraction
Indices of Refraction for Various Materials
Which One Is The Shortest Distance?
ABC
50 m
50 m
85 m
25 m
Which One Takes The Least Time?
ABC
Running Speed Is 10 m/s
Swimming Speed Is 2.5 m/s
5 s
20 s
8.5 s
10 s
Which One Takes The Least Time?
ABC
Fast
Slow
Light Behaves the Same Way!
•As light enters from a medium with a LOW index of refraction to one with a HIGH index of refraction, the ray bends TOWARDS the normal.
•As light enters from a medium with a HIGH index of refraction to one with a LOW index of refraction, the ray bends AWAY FROM the normal.
Refraction Simulator
http://interactagram.com/physics/optics/refraction/
The “Bent” Pencil
The “Bent” Pencil
Water
Actual Straw
Image of Straw
Full Reflection from Medium Interface!
Total Internal Reflection
Only occurs when light is going FROM a medium with a HIGHER index of refraction INTO a medium with a
LOWER index of refraction
http://interactagram.com/physics/optics/refraction/
The Critical Angle
The angle (with respect to the normal) at which the light totally internally
reflects is known as the critical angle.
The larger the index of refraction of the medium in which the light totally internally reflects, the smaller the
critical angle.
Critical Angles (Surrounding Medium: Air)
Internal Medium Refractive Index (n) Critical Angle [Deg.]
Water 1.33 48.8
Ethyl Alcohol 1.36 47.3
Quartz, Fused 1.46 43.2
Lucite 1.50 41.8
Glass, Crown 1.52 41.1
Glass, Flint 1.66 37.0
Zircon 1.92 31.4
Diamond 2.42 24.4
45° Glass Prisms> 41° (TIR)
Binoculars
Fiber-Optic Cables
Recommended