TOPIC
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EXAMPLES/APPLICATIONS/EXPLANATIONS
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HOW GALILEO
VIEWS INERTIA.
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HOW NEWTON EXPLAINS INERTIA
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Galileo’s idea is nearly the same as Newton in the stationary state.
However, he did not attribute this to zero net force but on the object’s
inertia.
Figure 13 Galileo's explanation of the
Law of Inertia
Galileo noted that objects rolled downhill goes uphill with the same
level it was released on. If one releases it on a flat plane with no uphill, the object will forever seek its uphill
height.
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The First Law of Motion, the Law
of Inertia states that a body can only be in two states of motion when ZERO
net force acts on it.
1)
A body is
stationary or not changing position with respect to the observer
2)
A body is
moving continuously at constant speed in one direction.
An example of this is when an
object on moving cart at constant speed suddenly stops. The object on top
continues its motion until another NON-ZERO net force stops it. Figure 14 Newton
assumes that bodies can move without force as long as inertia is available.
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HUYGEN’s
WAVE THEORY OF LIGHT
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NEWTON’s
CORPUSCULAR THEORY OF LIGHT
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During Newton’s lifetime, however, another theory of light was
forwarded. In 1678, the Dutch physicist and astronomer
Christian Huygens (1629–1695) showed
that a wave theory of light could also explain the laws of reflection and
refraction.
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Until the beginning of the 19th
century, scientists view light as a stream of particles emitted by a source that
stimulated the sense of sight on entering the eye. Newton’s corpuscular
theory, gave simple explanations of some known observations on the nature of
light such as reflection and refraction.
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Reflection as
explained by Wave Theory –waves
(as in waves in a basin or pond) bend their “wave fronts” as they encounter a
barrier (like the side of a container)
Reflected Wave (dashed
red)
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Figure 15
Reflection is when a wave reflects from a barrier, producing that distinctive
reflected wave.
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Reflection as
explained by Corpuscular Theory –
just like a Ping-Pong ball bounces of a surface, light corpuscles* (or little
bodies) bounce off surface unaffected by gravity or friction.
Incident Path (black
arrow)
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Reflected Path (dashed line)
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Figure 16
Reflection is just a particle bouncing off a surface
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Refraction as
explained by Wave Theory –
incident waves slow down as it enters a denser medium by bending
towards the point of entry.
Figure 17
Huygens’s refraction predicts that waves bend as they slow down when entering
a denser medium.
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Refraction by Corpuscular Theory –a light
corpuscle enters a denser medium it speeds
up, with the particle’s path bending towards the point of entry.
Figure 18
Refraction in corpuscular theory requires that the light particles must move
FASTER as it enters a denser medium
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HUYGEN’s
WAVE THEORY OF LIGHT
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NEWTON’s CORPUSCULAR THEORY OF LIGHT
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Interference as
explained by wave theory – This phenomenon happens when light waves passing
to double slit (narrow vertical hole) produce alternating bright and dark
patterns.
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This phenomenon, called “The double-slit experiment
was performed in 1801 by Thomas Young,”
This made light is a wave as a better theory, for 100 years.
Figure 19 Huygens’
theory predicts a band of alternating bright and dark is easily explained if
light is viewed as wave
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Interference as
explained by corpuscular theory:
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Corpuscular
theory has no explanation as why
light produces alternating bands of light and dark as it passes through a
double slit. The theory expects two bright spots or bright holes with the
shape of the slit.
Figure 20 Newton's
theory predicts two bright spots
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MAXWELL’s
WAVE THEORY OF LIGHT
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EINSTEIN’s PHOTON THEORY OF LIGHT
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The wave theory of light strengthened when James Clerk Maxwell used the concept
of waves to explain the origin of electromagnetic
waves as coming from
vibrating electric charges. It also happens that light is an electromagnetic wave, coming from vibrating electrons
in an atom. Example: when an
electron in an atom vibrates due to energy, they emit light as wave, a way of
expelling excess energy received.
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Another theory of light emerges
as the electromagnetic theory of light cannot explain why experiments show
that light energy corresponds to the frequency (color) of light wave rather
than light intensity (brightness). Max Planck and later Albert Einstein then
explained that light is more like a packet of energy (a quantum, a
“particle”) rather than wave.
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Figure 21 A vibrating charge releases waves
with the same wavelength as its vibrational displacement
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Figure 22 Electrons eject photons with the
same wavelength as the distance of energy "jump"
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WAVE
THEORY-WHAT DOES IT EXPLAIN?
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PHOTON THEORY-WHAT DOES IT EXPLAIN?
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This theory explains that light energy depends on the brightness of light,
§
meaning a brighter light, no matter what color has
more energy than a dimmer light of any color.
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This theory can’t explain “why a bright red light
cannot expose photographic films and a dim blue light can expose photographic
films?”.
§
Ultraviolet for example can burn human skin (sun
burn) since this light has higher frequency than violet or blue light.
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This theory called the quantum
theory of light explains that energy of light depends on the color of light. This is also called
the photon theory of light.
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It is
later found out that light energy is varies directly to the frequency (and
therefore color) of light.
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It means
that blue light has more energy than green light and green light has more
energy than red light.
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Higher
energy of light when its color is near blue or at blue, and lower energy when
its color is near red or at red.
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CURRENT
THEORY: LIGHT behaves either as a WAVE
or as a QUANTUM (PARTICLE)
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The success of electromagnetic theory made the modern world of
communications possible, from Radio-communications, TV and multimedia, the
internet, or any wireless communications, telecommunications became possible.
Light is undeniably a wave.
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The success of quantum theory in
expanding the field of chemistry, solid-state physics, high energy physics
and astrophysics is undeniably a
proof that light also behaves like a particle. The energy and momentum of each particle is expressed by the Planck’s
equation:
Energy: E = hf or hc/λ
Momentum: hf/c or h/ λ
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LIGHT IS A
WAVE
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LIGHT IS A PARTICLE (A PHOTON)
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Conclusion: Light behaves like a wave when situation requires it to
behave as a wave, otherwise on specific energy-based situation, light is a
photon, a particle of light. Situations like:
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Refraction - light waves changes speed as it
enters another medium and bends as
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Diffraction – light waves bend around corners
but can only be observed on small scale due to the size of the light wave
itself. Light wavelength varies from 770 nanometers to 480 nanometers. This
size is not easily observed by the naked eyes.
Figure 25 Diffraction of light
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Interference of light: two light sources or double slit
experiment shows that light cause alternating bands of light. This is
observable in nature.
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Light Polarization: Light waves can be filtered
according to the orientation of the filter. This cannot be explained if light
is a stream of particles.
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Conclusion: Light behaves like a particle/photon on situations that require light
to have high frequencies (and therefore high energy) and low intensity,
giving the photons a chance to exhibit its particle like properties.
Experiments like:
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Blackbody Radiation: Best explained by photon theory. The way energy is emitted by light
varies as a series of energy levels, not a continuous band of energy.
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Photoelectric Effect: Photon theory expects that a photon of higher frequency can eject
electrons from certain types of metals.
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X-Ray discovery: The production of
x-rays requires that electron energy corresponds to photon energy of light.
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Compton Effect: This experiment
discovered that light has momentum. Momentum is a property of particles.
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Phosphorescence and Iridescence are light producing
phenomena of materials and some living things that is best explained if light
is slowly emitted as photons (or quanta) of energy.
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