- Attachments : Lightning volcano
- We can not learn all about the Universe using “ light”. There is just too little of it. Even if we expand the meaning of ‘light” beyond visible light to the entire electromagnetic spectrum our vision is limited. 95% of the Universe does not respond to electromagnetic radiation or forces.
- And, there is a wide range of intensities of light. Obviously the farthest stars and galaxies are very dim as light intensity falls off at the inverse square of the distance. Long time exposures are required to collect enough light to gather an image.
- And, there is a wide range of frequencies of electromagnetic radiation. Light waves are a very small sliver from 700 to 900 nanometers wavelength. Electromagnetic radiation starts ate radio waves and goes through many octaves of wavelengths before reaching Gamma Rays that have the smallest wavelengths and the highest frequencies. We needed to invent special detectors to “see” everything beyond our little sliver of visible light.
- AM radio at 1230 Hertz on your dial has photons of energy of 7.42*10^-31 Joules.
- If you get a suntan with ultraviolet photos at 2.5*10^15 Hertz, or cycles per second, each photon is 17*10^-19 Joules of energy. Ultraviolet rays are 2.3 trillion times more powerful than the radio waves.
- An X-ray photon would be 1.6*10^-15 Joules of energy.
- Here is a quick summary of the wavelengths of “ light”:
-------------------- Gamma Rays -------------------- 0.01 nanometers
-------------------- X-rays ---------------------------- 1 nanometers
-------------------- Ultraviolet --------------------- 100 nanometers
-------------------- Visible ------------------------- 500 nanometers
-------------------- Infrared --------------------- 100,000 nanometers
-------------------- Microwaves -------------------- 1 centimeter
-------------------- Radio -------------------------- 1 meter
- A 100 watt light bulb has a photon energy of 2.05 *10^-19 Joules. Its temperature is 3,000 Kelvin. How many photons are coming off the light bulb?
- There are 480,000,000,000,000,000,000 photons coming off the light bulb every second. The human eye can detect as little as one photon. Unless you are old like me and you need at least 10 photons to detect the light.
- Light has power, amazing power. It is the light radiation coming from the core of a star that prevents the star from being collapsed by gravity.
- The radiation from the Sun that reaches the Earth ahs 1,000 watts of power per square meter. The sunshine hitting you is 45,000 times more powerful that the TV station’s electromagnetic signal that is also hitting you.
- Light gets its power from electricity and magnetism. The 1,000 watts of power coming from the Sun is a 900 volts per meter electric wave traveling perpendicular to a 0.3*10^-5 Tesla magnetic wave. The wave oscillation is side to side , not back and forth like a sound wave or a density wave.
- To convince you that the light power comes from electricity and magnetism we can go back to when this was discovered. It was discovered in Maxwell’s equations for an electric field and a magnetic field. His equations included the permeability of free space and the permittivity of free space. The product of these two parameters was the speed of light squared, 9 * 10^16. When Maxwell saw this he recognized it as the speed of light and concluded that light was an electromagnetic wave.
----------------- Permeability is the ratio of magnetic flux density to the magnetic field strength in free space.
------------------Permeability = 4 * pi* 10^-7 Tesla* meters / amperes
---------------- Tesla is a unit of magnetic induction equal one Weber of magnetic strength per square meter.
--------------- Permittivity is the ratio of electric displacement is a dielectric medium to the electric field strength.
--------------- Permittivity = 8.8 * 10^-12 Coulombs^2 / Newton * meters^2
---------------- Coulomb is a unit for the quantity of electricity equal to the charge transferred in one second across a conductor in which there is a constant current of one ampere.
------------- Newton is a unit of force that produces an acceleration of one meter per second on a mass of one kilogram.
- In Maxwell’s equation ------------- 1 / permeability * permittivity
-------------------------------------------- 1 / (4 * pi * 10^-7) * ( 8.8*10^-12)
-------------------------- 1 / 111 * 10^-19
-------------------------- 9 * 10^16 meters^2 / seconds^2
- That is the square of the velocity of light, ( 3 * 10^8 meters / second)
- It is crazy math and a rash of scientific units but it illustrates that light comes from electricity and magnetism. Maxwell made this discovery simply looking at his equations trying to understand how electricity and magnetism works.
- Who would have thought that placing a phone call for a dime would lead to a cell phone for $100 a month?
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(1) # 1288 “ We are immersed in electromagnetic radiation”
(2) # 1286 “ What makes electromagnetic waves into light?”
(3) # 726 “ Electric and magnetic forces”
(4) # 1043 “ The strangeness of light”
(5) # 621 “ Background radiation”
(6) # 36 “ What do you think is the oldest thing you can see?”
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707-536-3272, Saturday, January 28, 2012
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