Particle Theory of Light

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```					Particle Theory of Light
Group 1
II-Champaca

Ch 14 Kalle Pardilla
Ch 15 Justin Santos
Ch 17 Kenneth Tabafunda
Ch 23 Faye Dizon
Ch 24 Alison Estabaya
Corpuscular Theory of Light
I.     Corpuscular Theory of Light

II.    Reflection

III.   Refraction

IV.    Color and Polarization

V.     Flaws
Corpuscular Theory

Isaac Newton

Light is made up of streams of small
particles called corpuscles.

Opticks, 1704
Corpuscles
Small particles which make up light,
emit light in all directions
and has minute mass

If they have mass, how can they travel straight
horizontally under the influence of Earth’s
gravity?
The particles actually is in projectile
motion and follows the path of a
parabola!

So, why do we see light in a straight path?
We see light in a straight path, because the
corpuscles speed is very fast.

(300 meters in one microsecond)

In that time, it will fall in a distance of
5 x 10-12 m.

This distance is too small to be seen, so we see
light in a straight path.
Could this theory explain the properties of light?

Let’s see…
Reflection

The corpuscles bounce of a smooth
surface, this is the reflection of light,

Still adhering to the Law of Reflection:

Angle of Incidence = Angle of Reflection
It is just like an elastic and frictionless ball
bounces of a flat and smooth surface.
Reflection is an easy concept to tackle in
the particle model.

But, the key property for this theory is
refraction.
Refraction

Refraction of light can be summarized to be
the relationship of corpuscles and the
particles of matter it passes through.
When light is travelling through one medium,
the medium’s particles are spaced out equally
from the light particles.
Assume that there is force acting upon the
light particles and medium particles, which
cancel each other out, so light travels in a
straight line.

That is the case for one medium, what
happens if it encounters another medium?
When the light particles reaches a
boundary of a medium and another
medium, there will be difference in
the number of particles.

Because of this change, there will be a change
in net force, so the light particles will show
concise attraction to the medium with more
particles
Since, there is a force that drives the light
particles to the medium with more
particles, the corpuscle speed up in that
medium.

Can you visualize that to us?
Air

Net Force

Water
Substance State Refractive Index
Air Gas                1.000293
Ice Solid              1.31
Water Liquid           1.33
Ethyl Alcohol Liquid   1.36
Fluorite Solid         1.43
Quartz Solid           1.54
Salt Solid             1.54
Tourmaline Solid       1.62
Garnet Solid           1.73-1.89
Cubic Zirconia Solid   2.14 - 2.20
Diamond Solid          2.41
In general, the corpuscles has more velocity
in particles with higher density (more
particles) than those with less density
(less particles).

This is Refraction, in the particle theory of
light.
Other Properties of Light

Are there other properties which this theory
can explain?

Yes!
Color
Color is explained as a difference in the
masses of the color of each particle.

Red refracts least and violet refracts most
in the rainbow.

So the difference may be on the mass of
the color of the particles.
Red light particles has more mass than
violet light particles, so red has more
inertia than violet.

The one with more inertia will be deflected
less than the one with less inertia.

That’s why red refracts least and violet the
most, in prism.
Polarization
In simple terms, polarization is the change
of orientation of light.

Like left and right, or up and down

But if the particles are spherical then light
stays the same in all orientations
The explanation is that the particles are not
spherical.
The exact shape can’t be determined but it
may be:

or
Is this idea the most acceptable today?

No, it is not.

Why?
1850
Foucault disproved the idea of refraction
through the light particles.

How?
In this experiment,
Foucault showed that light travels slower in
water than in air, which is a complete
opposite of Newton’s explanation.
In this experiment, Newton’s Particle
Theory of Light collapsed, after this
decisive experiment.

Aside from this is there other explanation why
Newton’s theory is not accepted?
The other properties of light such as
diffraction and interference were not
explained in the theory.

This is another reason.

So, what now?
The collapse of this theory gave way to a
theory that light is WAVE…

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