- 2113 - Let there be light, let there be photons. The photon is
massless and only travels at one speed , the speed of light, 186,282 miles per
second. However, that speed is in a
vacuum, light travels through transparent medium at lower speeds. - When a photon hits an object it can be
reflected or absorbed. The transfer of
energy from the photon to the object is proportional to its frequency.
-
-
-
------------------ 2113 -
Let there be light,
let there be photons
-
- The photon is
electromagnetic radiation having wavelengths and frequencies ranging from radio
waves to gamma rays.
-
- We normally
do not think those are photons moving through the air powering your cell
phone. However, it is the photon of
electromagnetic energy traveling over the airways that carries your voice
conversations. Those are photons cooking
your food in the microwave. Those are
photons from distant stars that are lights in the night sky.
-
- The photon is
massless and only travels at one speed , the speed of light, 186,282 miles per
second. However, that speed is in a
vacuum, light travels through transparent medium at lower speeds.
-
- Light leaving the core of the Sun takes years
to reach the surface. Once at the
surface it takes only 8.3 minutes to reach us.
The space shuttle is fast at 25,000 miles per hour but that is under 7
miles per second. The frequency of
yellow light is 5 * 10^20 cycles per second.
Or, a wavelength of 2*10^-21 seconds per cycle.
-
- The eye
blinks in 10^-1 seconds. The camera
shutter clicks in 10^-3 seconds. The microprocessor
has a cycle time of 10^-9 seconds. A
laser pulse is 4^-15 seconds.
-
- The speed of
light is the speed regulator, nothing can go faster than the photon.
-
- Massless
particles MUST only travel at the speed of light. And, likewise, particles with mass must slow
down. Mass becomes energy that has just slowed
down enough for us to see it.
-
- When a photon
hits an object it can be reflected or absorbed.
The transfer of energy from the photon to the object is proportional to
its frequency.
-
-------------------
A photon’s momentum = 6.6*10^-34 * frequency / 3*10^8.
-
------------------- Or, 6.6*10^-34 / wavelength. p = h*f/c
p = h / w.
-
------------------
The Energy in a photon = 6.6*10^-34 * frequency. E = h*f.
-
- So, the higher the frequency of a photon the
more Energy it has. X-rays have more
energy than radio waves and blue light has more energy than red light.
-
- You would
think that a massless object would have no momentum. However, a photon does have momentum because
it carries energy and energy is the same as mass.
-
-----------------------E = mc^2. Energy = 9*10^16 * mass.
-
---------------------- Or, mass = Energy * .11*10^-16.
-
---------------------- Energy = momentum *
velocity.
-
----------------------- E = m*v^2.
-
- Photons have
both wave-like and particle-like behavior.
Or, better said, they have wave-like particle and particle-like wave
behavior.
-
- Albert
Einstein in 1905 first proposed that light, and therefore all electromagnetic
radiation, comes in quanta, or bundles of energy, called photons. Photons have no electric charge. They are a neutral particle.
-
- Whenever an electric charge is accelerated
photons are emitted. Whenever, an
electron in an atom drops from a higher shell to a lower shell a photon is
emitted. ( See Review 731 "The Electron"). Photons are emitted whenever matter and
anti-matter come together and are annihilated ( See Review 730 - "Antimatter").
-
- Since the
photon is massless you cannot use E = m*c^2, because you get zero energy. For massless particles you have to use E =
p*c. Where “p” is its momentum.
-
------------------------E^2 =
c^2*p^2 + m^2*c^4
-
The Force is the rate of change of momentum with
respect to time. F = dp/dt
-
- In 1900 the electromagnetic
energy radiation calculated from the temperature of an object was:
-
-------------------
E = 8*pi*f^2*k*T/c^3 , where
k is Boltzman’s Constant.
-
But, in 1905 the formula changed due to the discovery
of Planck’s Constant:
-
------------------- E = 8*pi*f^3/c^3 * (e^h*f/k*T - 1)
-
-------------------, where “h” = 6.6*10^-34
kilograms*m^2/sec.
-
- Photons can
propagate with left-handed or right-handed rotation , or polarization. That is what makes Polaroid glasses work as
sunglasses.
-
- Photons have an integer spin = 1. Therefore they are Bosons and obey the
Bose-Einstein statistics in probabilistic behavior.
-
- In contrast,
electrons have a spin = ½ . They are
Fermions and obey the Fermi-Durac statistics of probabilistic behavior and
Pauli’s Exclusion Principle.
-
- All these
formulas, give me a break, how does any of this stuff work and how can I use
it?
-
- Answer: Look up in the night sky and see a star. Use
a wattmeter and measure the intensity of the light coming from that star. The wattmeter peaks at 560 nanometers
wavelength and the intensity is 1.6 * 10^-9 watts / meter^2.
-
- 560 nanometers is the color of blue-green
light. The light from that star has
traveled over 1 billion lightyears and is therefore 1 billion years old. In order to see that star how many of these
old photons are entering your eye?
-
----------- The
energy of one photon = E
= h*f
-
----------- f
= frequency = c / wavelength
-
-----------
The intensity in watts is the number of photons times the energy of each
photon.
-
-----------
N = I / E
-
------------
N = I * w / h * c
-
------------
N = 1.6 *10^-9 watts / m^2 * 5.6
* 10^-7 m / 6.64*10^-34 kg*m^2/sec^2 * 3*
10^8 m
-
-------------
N = .44 kg
m/sec^2 * sec / kg*m^3 /sec^2
-
--------------
N = .44 * ^10 photons / m^2 / sec
-
--------------
N = 4.4 billion photons / meter^2 / sec
-
- The eye has a
pupil that is ½ centimeter in diameter.
-
-------------
Diameter = .005 meters
-
- The area of
the pupil = pi * r^2
= 3.14 * (2.5* 10^-3)^2 m^2
-
---------------Area = 2 * 10^-5 m^2
-
- The number of
photons entering the eye = 4.4*10^9
photons / m^2 * sec * 2 * 10^-5 m^2 = .9 *
10^5 photons / sec
-
-------------
The eye is detecting 90,000 photons / second.
-
- The eye is
capable of detecting 25 photons / second of red light. That is enough energy to trigger the optic
nerve in the retina. With a night
adapted eye, after 20 minutes in darkness, the eye’s chemistry changes and it
is able to detect as few as 5 photons / second of starlight.
-
- In midday sunlight reaches 1400 watts /
m^2.
-
---------------
N = 1.4 *10^3watts / m^2 * 5.6
* 10^-7 m / 6.64*10^-34 kg*m^2/sec^2 * 3*
10^8 m
-
-----------------N
= .39 * 10^22
-
-----------------The number of photons entering the
eye in daylight = .39
* 10^22 photons / m^2 * sec * 2
* 10^-5 m^2 = .79 * 10^17 photons / sec.
-
-----------------
79,000,000,000,000,000 photons enter the eye each second.
-
------------------
The eye has a dynamic range of 18 powers of 10. It truly is a remarkable instrument.
-
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to
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---
Some reviews are at:
--------------
http://jdetrick.blogspot.com -----
--
email feedback, corrections, request for copies or Index of all reviews
--------------------- Wednesday, October 10,
2018 -------------------------
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