Models
 Used for the usefulness of things we cannot see, and
is ever-changing
 For example..the model of the atom, our current
model of light, the elegibunnybutterduck
The Nature of Light
The History of the Nature of Light
How would light act if it were a particle, if it were a wave ?
Light Is a Particle! (Sir Isaac Newton)
 Newton thought that light was a particle because the
edges of the shadows it created was extremely sharp
and clear.
Light Is a Wave! ( Christian Huygens)
 About the same time as Newton, Dutch physicist,
Christian Huygens, believed that light was made up
of waves vibrating up and down perpendicular to the
direction of the light travels. It explained diffraction
and could be demonstrated through
experimentation.
Light Is Also a Particle! (Einstein)
 The theory of light being a particle completely
vanished until the end of the 19th century when
Albert Einstein revived it.
 Einstein believed light is a particle (photon) .
 Scientists have combined both theorys
The Dual Nature of light is the accepted and
current concept of the nature of light.
The Dual Nature of Light
 Light is a form of energy.
 Sometimes it behaves like a particle and
sometimes it behaves like a wave .
 For this reason, light is said to have a dual nature
The properties of light can be summarized into
two groups…with its dual nature
3 "particle" properties
and 3 "wave" properties
1) Travels in straight lines
2) Reflection (changes
direction)
3) Refraction (bends, in
going from one material to
another)
1) Interference (waves
"superpose" and pass right
through each other)
2) Diffraction (waves "spill
over" the edges of their
obstructions)
3) Polarization (eliminating
one of light's "fields")
The Dual Nature of Light
Particle properties of light
difficult to explain using the
wave theory
Wave properties of light
difficult to explain using the
particle theory
Where does the Photoelectric Effect fall, proof of
particle or wave ?
 The various properties of light, which is a type of
electromagnetic wave, are due to the behavior of
extremely small particles called photons that are
invisible to the naked eye.
The Dual Nature of Light
State the three “wave” properties of light
Interference
Diffraction
Polarization
The Dual Nature of Light
State the three “particle” properties of light
1) Travels in straight lines
2) Reflection
3) Refraction
The Dual Nature of Light
In your own words, define a photon.
 A photon is a packet of energy traveling at a speed
of 3 x 108 m/s
 Each color is a different photon having a different
amount of energy.
 A photon of red light has the least amount of energy,
 while a photon of violet light has the greatest amount
of energy.
The Dual Nature of Light
Define light and explain what is meant by the phrase
"the dual nature of light“
Light is a form of energy and has a dual nature. This
means that light possesses both particle properties
and wave properties.