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An Historical Review
of Natural Phenomena and Models
That Demonstrates
Wave-Particle Duality
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Reflection and Refraction
The Phenomenon
Light waves passing through one
transparent medium into another are
partly reflected and partly transmitted.
There is a constant ratio between the
angles at which the rays are hitting,
reflecting, and passing.
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Reflection and Refraction
The Model
Newton, ~ 1650
Light rays consist of particles that obey the
laws of classical mechanics.
Hugens, ~ 1650
Light rays consist of pinpoint wave sources.
The direction of the wave front determines
the direction of the ray.
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Circumvention
The Phenomenon
Fresnel ~ 1800
Light can “circumvent” obstacles and
illuminate regions that should have
been shadowed
(according to the laws of
Geometrical Optics)
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Interference
The Phenomenon
Young ~ 1800
Light passing through two slits
(d1mm) displays a pattern of
alternating dark and light stripes on a
screen placed in front of these two
slits.
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Circumvention and Interference
The Model
1. Light consists of waves, which are
periodic functions
2. The superposition of two waves is also a
wave function
3. The light intensity is proportional to the
square amplitude of the wave function
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sin  = m  / d
Diffraction Grating
The Model
A light ray passing through
a ruled slide
(d  1µ) splits into a
number of rays
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Diffraction Grating
The Model
A constructive interference occurs
into specific directions. The
difference in optical paths for the
rays coming from each slit is an
integer multiple of the wavelength.
d sin  = m 
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

Electromagnetic Radiation
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The Phenomenon
The Model
Hertz 1888
An electric current alternating
within a conductor produces a
radio-wave propagating at the
speed of light
Maxwell 1864
Light is an electromagnetic
wave
The Photoelectric Effect
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The Phenomenon
The Model
Mulliken 1916
A surface of metal illuminated by
light ejects electrons. The kinetic
energy of the electrons is
proportional to the frequency of the
impinging light.
Einstein 1905
Light is composed of particles
whose energy is:
The Compton Effect
The Phenomenon
Compton 1923
A laser ray, directed opposite to the
flow of a beam of hot sodium
atoms, cools the atoms. This
occurs due to momentum transfer
from the light to the moving atoms.
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The Model
Light is composed of particles
with the following momentum:
Cathode Radiation
The Phenomenon
Thomson 1897
Cathode rays are deflected off their
pathway by magnetic and electric
fields
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The Model
The rays are composed of particles
having a negative mass and charge
The Oil Drop Experiment
The Phenomenon
Mulliken 1913
Sprayed oil droplets become
electrically charged by an integer
multiple of a value ‘e’ charge
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The Model
The charge stems from particles,
of which each is charged by the
elementary charge ‘e’
The De Broglie Wave
The Model
De Broglie 1924
Particles can possess a wave-like
behavior. The particles’ behavior is
analogous to light when it behaves
like a particle.
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The wavelength corresponding
to a particle of mass ‘m’ and
velocity ‘v’ is:
Diffraction of Electrons from a Crystal
The Phenomenon
Davison-Gremer 1927
When a beam of electrons,
accelerated in a low electric field,
hits a Ni crystal, it creates a
diffraction pattern.
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Diffraction of Electrons from a Crystal
The Model
Electrons are waves with a
wavelength
The three directions of the crystal
create three intersecting diffraction
patterns
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Diffraction of Atoms from a Crystal
The Phenomenon
Stern 1930
A beam of particles (He, H2)
hitting a LiF crystal splits into
several rays.
He 100oK
He 300oK
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20o 15o 10o 5o 0o 5o 10o 15o 20o
Atom Diffraction from a Crystal
The Phenomenon
A supersonic beam of He particles hitting a GaAs crystal splits
into numerous rays
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