- 3620 - PHOTONS - a full range of energy? The photons are electromagnetic radiation having wavelengths and frequencies ranging from radio waves to gamma rays. The visual radiation is just small part of this electromagnetic spectrum. We normally do not think those same photons are moving through the air powering your cell phone.
--------------------- 3620 - PHOTONS - a full range of energy?
- When our eyes see things what is really happening is that our eyes are collecting photons of light. Our brains turn that collection of photons into visual images.
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- It is the photon of electromagnetic energy traveling over the airways that carries our voice conversations. Those are photons cooking our food in the microwave. Those are photons from distant stars that are lights in the night sky. Photons are everywhere.
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- The photon is massless and only travels at one speed , the speed of light, 186,000 miles per second. However, that speed is in a vacuum, light travels through transparent matter at lower speeds because it is absorbed and retransmitted reportedly at a slower rate.
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- 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..
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- The frequency of yellow light is 5 * 10^20 cycles per second. Or, 2*10^-21 seconds per cycle.
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- The eye blinks in 10^-1 seconds.
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- The camera shutter clicks in 10^-3 seconds.
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- The Pentuim processor as a cycle time of 10^-9 seconds.
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- A laser pulse is 4^-15 seconds. The speed of light is the speed regulator, nothing can go faster than the photon.
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- Massless particles MUST only travel at the speed of light. And, likewise, particles with mass must slow down. Mass comes from energy that has slowed down enough for us to see it. Stop and think abut that for a while. Mass is just light energy at a slower speed.
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- 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.
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------------------- 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.
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- 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.
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- 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.
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----------------- E = mc^2.
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----------------- Energy = 9*10^16 * mass.
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----------------- Mass = Energy * 0.11*10^-16.
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------------------ Energy = momentum * velocity. E = m*v^2.
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- 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.
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- 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 2557 “The Electron“).
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- Photons are emitted whenever matter and anti-matter come together and are annihilated (See Review 2562 “Antimatter“).
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- Since the photon is massless you can not use E = m*c^2, because you get zero energy. m = zero. For massless particles you have to use E = p*c. Where “p” is its momentum.
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------------------------ E^2 = c^2*p^2 + m^2*c^4
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- The Force is the rate of change of momentum with respect to time. F = dp/dt
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- In 1900 the electromagnetic energy radiation calculated from the temperature of an object was:
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------------------- E = 8*pi*f^2*k*T/c^3, where k is Boltzman’s Constant.
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- But, in 1905 the formula changed due to the discovery of Planck’s Constant:
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------------------ E = 8*pi*f^3/c^3 * (e^h*f/k*T - 1),
where “h” = 6.6*10^-34 kilograms*m^2/sec.
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- Photons can propagate with left-handed or right-handed rotation , or polarization. That is what makes Polaroid glasses work as sunglasses.
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- Photons have an integer spin = 1. Therefore they are Bosons and obey the Bose-Einstein statistics in probabilistic behavior.
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- In contrast, electrons have a spin = ½ . They are Fermions and obey the Fermi-Durac statistics of probabilistic behavior and Pauli’s Exclusion Principle.
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- All these formulas, give me a break, how does any of this stuff work and how can I use it?
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- 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.
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- 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?
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----------- The energy of one photon = E = h*f
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----------- f = frequency = c / wavelength
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----------- The intensity in watts is the number of photons times the energy of each photon.
----------- N = I / E
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------------ N = I * w / h * c
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------------ 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
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------------- N = .44 kg m/sec^2 * sec / kg*m^3 /sec^2
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-------------- N = .44 * ^10 photons / m^2 / sec
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-------------- N = 4.4 billion photons / meter^2 / sec
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- The eye has a pupil the 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
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--------------- Area = 2 * 10^-5 m^2
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- 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
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------------- The eye is detecting 90,000 photons / second.
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- 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.
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--------------- 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
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-----------------N = .39 * 10^22
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-----------------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.
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----------------- 79,000,000,000,000,000 photons enter the eye each second.
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------------------ The eye has a dynamic range of 18 powers of 10.
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- It truly is a remarkable instrument.
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July 5, 2022 - PHOTONS - a full range of energy? 733 2113 3620
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--------------------- --- Friday, July 8, 2022 ---------------------------
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