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Chapter 22
Reflection and Refraction of Light
1. Dual nature of light
2. Geometric optics
3. Reflection and Refraction
4. Dispersion
5. Huygen’s Principle
6. Total Internal Reflection
A Brief History of Light
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1000 AD
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Newton
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It was proposed that light consisted of tiny
particles
Used this particle model to explain
reflection and refraction
Huygens
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1678
Explained many properties of light by
proposing light was wave-like
A Brief History of Light,
cont
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Young
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1801
Strong support for wave theory by
showing interference
Maxwell
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1865
Electromagnetic waves travel at the
speed of light
A Brief History of Light,
final
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Planck
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EM radiation is quantized
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Implies particles
Explained light spectrum emitted by
hot objects
Einstein
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Particle nature of light
Explained the photoelectric effect
The Particle Nature of
Light
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What is a photon?
How do I calculate its energy?
Can photon have a wave nature?
What about experiments to test
such theories?
Can a single experiment test dual
nature of light?
Ray Approximation &
Geometric Optics
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What is a wave
front?
What is a Ray?
What is the
purpose of a ray?
Specular and Diffuse
Reflection
Law of Reflection
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What is it?
Example
1.
Two mirrors make an angle of
120° with each other. A ray is
incident on mirror M1 at an angle
of 65° to the normal. Find the
angle the ray makes with the
normal to M2 after it is reflected
from both mirrors
Refraction of Light
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What is
refraction?
Snell’s Law
Two cases of Refraction
The Index of Refraction
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What is index of
refraction?
How do I calculate
it?
What are its units?
Some typical
examples
What happens when
light passes from
one medium to
another?
An alternate formula
Some Indices of Refraction
Example
1.
An underwater scuba diver sees the
Sun at an apparent angle of 45.0°
from the vertical. What is the actual
direction of the Sun?
Example
1.
Find the speed of light in flint glass.
Dispersion
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What is dispersion?
Wavelength vs. n for
visible light.
How does Snell’s law
play into this?
Refraction in a Prism
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What is angle of
deviation, δ?
Example
1.
The index of refraction for violet light in
silica flint glass is 1.66 and that for red
light is 1.62. What is the angular dispersion
of visible light passing through a prism of
apex angle 60.0°, if the angle of incidence
is 50.0°.
Prism Spectrometer
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What is
How do
What is
What is
a spectrometer?
we use it?
a spectrum?
it useful for?
Reflection, Refraction and the
Rainbow
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Why do we see the rainbow?
Kirchhoff’s Laws of Radiation (1)
1.
A solid, liquid, or dense gas excited to emit light
will radiate at all wavelengths and thus produce a
continuous spectrum.
Kirchhoff’s Laws of Radiation (2)
2. A low-density gas excited to emit light will
do so at specific wavelengths and thus
produce an emission spectrum.
Light excites electrons in
atoms to higher energy states
Transition back to lower states emits light at specific
frequencies
Kirchhoff’s Laws of Radiation (3)
3. If light comprising a continuous spectrum
passes through a cool, low-density gas,
the result will be an absorption spectrum.
Light excites electrons in
atoms to higher energy states
Frequencies corresponding to the transition energies are
absorbed from the continuous spectrum.
The Spectra of Stars
Inner, dense layers of a
star produce a continuous
(blackbody) spectrum.
Cooler surface layers absorb light at specific frequencies.
=> Spectra of stars are absorption spectra.
Christian Huygens
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1629 – 1695
Best known for
contributions to
fields of optics and
dynamics
Deduced the laws of
reflection and
refraction
Explained double
refraction
Huygen’s Principle
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What is Huygen’s
principle?
How do I apply it for
plane waves?
How do I apply it to
spherical waves?
What is the
difference between
spherical and plane?
Why do I even need
to know it?
Total Internal Reflection
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What is Total
internal reflection?
What is critical
angle?
How do I calculate
it?
When is total
internal reflection
possible?
Example
1.
A small underwater pool light is 1.0m
below the surface. The light emerging
from the water forms a circle on the
water surface. What is the diameter of
this circle?
Total Internal Reflection and
Fiber Optics
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Applications
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Surgical techniques
Telecommunications
Industry
What are the
advantages?
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Noise
Light loss