Theories of Light Is light made up of particles or waves?
Slide 3
Whether or not light was composed of particles of waves was the
subject of vigorous debate.
Slide 4
Particle v. Wave Theories Sir Isaac Newton proposed that white
light was actually made up of colored particles which combined to
appear white. The theory that light was composed of particles was
known as the corpuscular (particle) theory.
Slide 5
Newton experimented with prisms and observed that what light
was composed of a spectrum of colors. He conducted many experiments
and at one point pushed a bodkin needle into his eye socket,
putting pressure on his eyeball to see how that would effect his
vision.
Slide 6
Newton s book on light was first published in 1704.
Slide 7
Slide 8
Slide 9
Christian Hyugens published his Treatise on Light in 1690, in
which he proposed that light traveled in the form of waves. (ALSO:
Huygens made many astronomical discoveries. He was first to use a
pendulum to regulate a clock. In 1659 he derived the now standard
formula for the centripetal force, exerted on an object.
Slide 10
Slide 11
Light is a form of Electromagnetic radiation. Max Planck, at
the turn of the 20 th century, proposed that light, as well as some
other forms of radiation, are generated by interacting electric and
magnetic fields.
Slide 12
Planck developed the quantum theory in which energy is emitted
from atoms in discrete units called quanta.
Slide 13
Einstein applied Plancks idea to the photoelectric effect in
which he proposed that atoms absorbed or emitted energy in bundles
called photons. Therefore, light was made up of quanta called
photons.
Slide 14
Louis de Broglie proposed that all particles, as well as
photons, act like standing waves which vibrate at specific and
discrete or quantized frequencies.
Slide 15
Erwin Schrdinger developed a generalized equation to describe
the particle-wave characteristic. The Schrdinger equation is the
fundamental equation of physics for describing quantum mechanical
behavior. It is also often called the Schrdinger wave equation, and
is a partial differential equation that describes how the wave
function of a physical system evolves over time.- Science
World
Slide 16
Niels Bohr proposed the Copenhagen interpretation of quantum
theory, which asserts that a particle is whatever it is measured to
be (for example, a wave or a particle), but that it cannot be
assumed to have specific properties, or even to exist, until it is
measured. Einstein & Bohr
Slide 17
In short, Bohr was saying that objective reality does not
exist. This translates to a principle called superposition that
claims that while we do not know what the state of any object is,
it is actually in all possible states simultaneously, as long as we
don't look to check.
Slide 18
Slide 19
The Schrdingers cat paradox.
Slide 20
Slide 21
Slide 22
IN SUMMARY: Light is a type of electromagnetic wave, which
means that it is produced by an interaction of oscillating electric
and magnetic fields.
Slide 23
The current model of light incorporates aspects of both
particle and wave theories. This is known as wave particle duality.
AND
Slide 24
Light is emitted from luminous bodies in little packets of
energy called photons. Since each photon is associated with light
waves of specific frequencies, it can be said that there is a
definite quantity of energy proportional to each frequency known as
quanta. AND
Slide 25
Particle-like behavior: photons can collide and interact with
electrons and other tiny particles of matter Wave-like behavior:
photons move through space in a probability wave which specifies
the likelihood that a photons energy will be found at a given point
on a wave front. (Interacting probability waves account for
interference, diffraction, and other wave-like properties of
light.) AND:
Slide 26
Slide 27
How the human eye works FromLiveScience.com The cornea a
transparent structure found in the very front of the eye, helps to
focus incoming light. Behind the cornea is a colored ring-shaped
membrane called the iris.
Slide 28
The iris has an adjustable circular opening called the pupil,
which can expand or contract depending on the amount of light
entering the eye. A clear fluid called the aqueous humor fills the
space between the cornea and the iris.
Slide 29
Situated behind the pupil is a colorless, transparent structure
called the crystalline lens. Ciliary muscles surround the lens. The
muscles hold the lens in place but they also play an important role
in vision. (When the muscles relax, they pull on and flatten the
lens, allowing the eye to see objects that are far away. To see
closer objects clearly, the ciliary muscle must contract in order
to thicken the lens.)
Slide 30
The interior chamber of the eyeball is filled with a jelly-like
tissue called the vitreous humor. After passing through the lens,
light must travel through this humor before striking the sensitive
layer of cells called the retina.
Slide 31
The retina is the innermost of three tissue layers that make up
the eye. The outermost layer, called the sclera, gives most of the
eyeball its white color. (The cornea is also a part of outer
layer.) The middle layer between the retina and sclera is called
the choroid. (The choroid contains blood vessels that supply the
retina with nutrients and oxygen and removes its waste
products.)
Slide 32
Embedded in the retina are millions of light sensitive cells,
which come in two main varieties: rods and cones. Rod and Cone
Slide 33
Rods are good for monochrome vision in poor light, while cones
are used for color and for the detection of fine detail. Cones are
packed into a part of the retina directly behind the retina called
the fovea. Blue = Nuclei
Slide 34
When light strikes either the rods or the cones of the retina,
it's converted into an electric signal that is relayed to the brain
via the optic nerve. The brain then translates the electrical
signals into the images we see.
Slide 35
The Luminous and the Illuminated Anything that gives off light
is luminous. Anything upon which light falls becomes illuminated.
The hand is illuminated by the luminous bulb.
Slide 36
The strength of a light source is called the luminous
intensity, measured in units called candelas. A candela is the rate
at which 1/60th of a square centimeter emits light. A 40 watt
incandescent bulb has an intensity of about 35 candelas.
Slide 37
Alternatively: The rate at which light falls upon a unit area
of a surface is called the intensity of illumination and is
measured in lumens.
Slide 38
Intensity of Illumination or Luminous flux If a 1 candela light
source is placed at the center of a imagined sphere-shaped area of
1m radius, the rate at which light falls upon 1 square meter of the
inner sphere surface is 1 lumen.
Slide 39
The Luminous flux will stay the same for a given light source.
(Luminous flux is the same for every sphere.) But, the amount of
light falling upon a surface decreases with the distance from the
light source. Luminous flux divided by the area of the surface,
which is called the illuminance (measured in lm/m 2 or lux)
decreases as the radius squared when moving from the light source.
Serway/Faughn Physics pg 446
Slide 40
What is the difference between Lumens & Lux? Lumens, also
known as luminous flux, is the measure of the perceived power of
light from a natural or artificial light source. In simple terms it
is the measurement of how bright a bulb or tube is. Whether you are
1 meter away or 100 meters away from a light source it is still
emitting the same amount of lumens. Lux is the measure of the
apparent intensity of light hitting or passing through a surface at
a given distance. A light source 1 meter away will have a far
greater lux than if you were 10 meters away. So in summary the
difference between the units Lumen and Lux is that Lux takes into
account the area over which the luminous flux is spread at a FIXED
distance. Whereas Lumens is the amount of light coming from a light
source irrespective of the distance. Daylightco.com
