All the light of the electromagnetic spectrum
| || Automatic translation|| ||Category: light and photons|
Updated June 01, 2013
Visible light is only a small range of electromagnetic vibrations found in the electromagnetic spectrum. The Earth's atmosphere allows only a portion of this radiation. This filter is a very important role in the evolution of organic life on Earth. Shortwave is absorbed in the atmospheric layers and long waves are reflected, which allows larger waves of terrestrial transmitters to be picked up at long range. The existence of the radio window has enabled the development of radio astronomy.
The nature of light is the quantum mechanics to which it is both a wave and a particle. The light has a wavelength, which determines the color, eg Red emits in the wavelength of 700 nanometers, the Orange 650 nm, 600 nm Yellow, Green 550 nm, Blue 500 nm Violet 450 nm. This window is chosen by the human eye to specialize. But the invisible light is spread over a larger electromagnetic field.
Maxwell found that light is an electromagnetic wave and there is no reason to limit the wavelength thereof at the interval corresponding to the spectrum of visible light, all the spectrum is light. Since then, it was observed that the electromagnetic wavelengths vary between 10-16 m and several thousands of kilometers. Different windows of the electromagnetic spectrum are characterized by a wavelength, but also by a range of frequencies defined.
Frequency is the number of electromagnetic oscillations that pass through a given point in one second. it is expressed with the unit of frequency what is the hertz. Over the wavelength is shorter, the frequency is high to very high frequencies. The frequency is inversely proportional to the wavelength.
nota: Between wavelength (λ) and frequency (ν) is the following relationship: ν = c / λ
ν = wave frequency in hertz
c = speed of light in vacuum in m/s
λ = wavelength in meter
| || |
Image: The electromagnetic spectrum includes all windows of light, it extends theoretically zero to infinity, on frequency or wavelength, continuously.
| || || || |
A radio wave is an electromagnetic wave whose frequency is lower than 3000 GHz, a wavelength greater than 0.1 m.
The sound is a vibration of matter, or radio waves are electromagnetic waves of the same nature as light, i.e. disturbances of electric and magnetic fields.
Unlike sound waves, which require a material medium to propagate the electromagnetic waves them travel better in a vacuum.
The sound goes only 300 m / s, while the electromagnetic waves along at the speed of light is 299,792,458 m/s. A radio transmitter antenna produces light as a neon, but it's like radio waves that our eyes or our ears can perceive.
Like all electromagnetic waves, radio waves propagate through empty space at the speed of light and with an attenuation proportional to the square of the distance traveled by the equation of telecommunications.
In the atmosphere, they undergo further mitigations related to precipitation, and can be reflected or guided by that portion of the upper atmosphere called the ionosphere.
Electromagnetic waves are attenuated or deflected by the obstacles, depending on their wavelength, the nature of the material, its shape and size.
For simplicity, a conductive material will have a reflection effect, while a dielectric material will produce a deviation, and the effect is related to the ratio between the size of the object and the wavelength.
| || || || |
Microwaves are electromagnetic waves of intermediate wavelength between infrared and radio waves. Microwaves are used in many applications, radio, radar, television, internet...
The best known are the microwaves generated in our ovens, they are among the light waves have less energy, less energy than visible or infrared waves that emerge from a conventional oven.
Their extraordinary efficiency is due to an effect both subtle and violent called resonance.
What we eat has a very large proportion of water and water molecules have a natural frequency that corresponds to that of microwaves. Shaken by the microwaves, water molecules resonate and this molecular agitation increases the temperature of the water contained in food. Microwaves have the advantage of not heating the material, while the oven is at room temperature.
The energy penetrates almost instantly in the target, the heating time and industrial cycles are significantly shortened.
||1 to 2 GHz
||30 to 15 cm
||2 to 4 GHz
||15 to 7.5 cm
||4 to 8 GHz
||7.5 to 3.75 cm
||8 to 12 GHz
||3.75 to 2.5 cm
||12 to 18 GHz
||2.5 to 1.6 cm
||18 to 26 GHz
||16.6 to 11.5 mm
||26 to 40 GHz
||11.5 to 7.5 mm
||30 to 50 GHz
||10 to 6 mm
||40 to 60 GHz
||7.5 to 5 mm
||46 to 56 GHz
||6.5 to 5.3 mm
||56 to 100 GHz
||5.3 to 3 mm
Image: The microwave range is divided into different bands, depending on various engineering applications (astronomy, weather radar, satellite broadcasting, telecommunications, radio, television, radio and data, satellite internet...
| || || || |
Infrared waves « below red » are electromagnetic waves of wave lengths intermediate between the microwave and lower than those of visible red light waves.
The wavelength of the infrared ranges between 780 nm and 1 000 000 nm, that is to say 1 millimeter.
Infrared is used for heating materials in the automotive, food processing, textiles, body care.
The LEDs used in TV remotes or other devices also emit infrared radiation.
In astronomy, the infrared radiation is used in observation satellite (IRAS, ISO, Wire, Spitzer, ASTRO-F, Herschel) to see through the dark clouds of dust that do not emit visible light.
When looking at a sunlit building, we see through the light reflected on the walls but on a dark night, we see nothing. Yet every warm body emits light but is not visible with our eyes. This is why the audits of energy savings seeking heat loss in buildings with infrared cameras (see picture opposite).
The military also uses infrared through glasses that let you see the hot body (the enemy) at night.
Image: Infrared radiation (IR) is electromagnetic radiation of a wavelength greater than that of visible light but shorter than microwaves.
Image: hunters energy waste, carry out thermographies, the early morning and in cold weather, on the facades of buildings to highlight the most significant energy losses.
| || || || |
Visible light is only a small range of electromagnetic vibrations that we find in the electromagnetic spectrum.
Light refers to electromagnetic waves visible to the human eye, they are included in the wavelengths of 0.38 to 0.78 micron. 380 nanometers for violet to 780 nm for red. The light is closely linked to the concept of color.
Newton proposed for the first time in the seventeenth century a circle of chromatic colors based on the decomposition of white light. Sunlight is the primary source of energy emitted by the sun. It supplies terrestrial ecosystems via photosynthesis.
The Rainbow is a natural phenomenon that conveys light spectrum In physics, the spectrum is the entire radiation emitted by a source, representing the radiation according to their wavelength. For example, the solar spectrum is composed of all the colors of the rainbow in the sky, the spectrum of a sound source is the set of sound emitted fluctuations. The electromagnetic spectrum is the decomposition of electromagnetic radiation according to its components in terms of associated frequencies. of the light, by reflection in the water droplets suspended in the air, such as clouds, for example.
On the picture against the rainbow sky appears to us as a composition of colors, including red is outside the arc and violet on the inside, between these two colors are, red, orange, yellow, green and blue.
All drops illuminated by the sun appear colored to an observer who is situated in an angle "sun-drop-eye" of approximately 42°.
When the sun is low on the horizon, over the arch rises in the sky and vice versa. When the sun rises above 41° to the horizon, the rainbow sky is no longer visible, which is why in rainbows are visible only in the morning or evening, by an observer who is situated at the level of the sea. Sometimes, when the rainbow sky is very bright, a secondary arc is observed much paler.
Image: the spectrum of visible light ranging from infrared to ultraviolet, corresponds to wavelengths of 400 nanometers in the violet at 800 nanometers in the red, i.e. 0.4 x 10-6 to 0.8 x 10-6 meter. nota: Between the wavelength (λ) and frequency (ν) the following relationship: ν = c / λ where c is the speed of light is ≈300 000 000 m/s.
Infrared are in the invisible between 800 and 1400 nm and ultraviolet between 100 and 400 nm, also in the invisible.
Example, calculating the frequency of the red (ν = c / λ):
ν = 300 x 106 / 0.8 x 10-6 = 375 x 10-12 Hz or 375 terahertz
| || || || |
Ultraviolet (UV) radiation is electromagnetic radiation of a wavelength between that of visible light and the X-ray The range of UV radiation is often subdivided into UVA (400-315 nm), UVB (315-280 nm) and UVC (280-10 nm).
UV-A emitted by the Sun, nearly 95% of UV radiation reaching the Earth's surface.
UV-B, responsible for tanning, have significant biological activity, but does not penetrate beyond the superficial layers of the skin. Part of solar UV-B are filtered by the atmosphere.
UV-C, are the most harmful UV rays, but are completely filtered by the ozone layer of the atmosphere and thus do not reach the surface of the Earth. UV-C lamps are used in biology laboratory to sterilize rooms or units.
Nearly 5% of the sun's energy is emitted as UV radiation. The vision of insects, like bees, extends the spectrum of ultraviolet (UV-A).
Black light or Wood's light (inventor Robert William Wood), is composed of a light violet and ultraviolet (around 375 nm), with a slight peak around 405 nm wavelength which makes it a bit illuminating.
nota: The range of UV radiation is divided into UVA photons which have a wavelength between 400 and 315 nm, UVB (315-280 nm) and UVC (280-100 nm). If part of the solar UVB are filtered by the atmosphere, the UVC is they filtered through the ozone layer of the atmosphere and therefore do not theoretically the surface Earth.
| || || || |
X-rays are electromagnetic waves at high frequency between the ultraviolet rays and gamma waves. Discovered in 1895 by German physicist Wilhelm Roentgen, these electromagnetic waves have the property through our body without too much difficulty. X-rays are electromagnetic waves at high frequency whose wavelength is between approximately 5 picometers and 10 nanometers.
Ionizing radiation is used in many applications including medical imaging and crystallography.
Medical radiography is based on the fact that the bones are a little more radiopaque than the flesh.
It is also a range of radiation is widely used in astrophysics.
X-rays and gamma rays are similar in nature (consisting of photons), but are produced differently.
X-rays are produced by electronic transitions (change of orbit of electrons) while the gamma rays are produced during the radioactive decay of atomic nuclei.
X-rays easily penetrate soft matter, the solid sparse consisting of light elements like carbon, oxygen and nitrogen.
They are easily absorbed by the hard material consists of heavy elements through air and the atmosphere.
| || || || |
The gamma rays are photons of very high energy (beyond 100 keV) sufficient to remove an electron from its orbit.
They have a very short wavelength, less than 5 picometers, and can be produced by nuclear disintegration, especially in the breasts of massive stars at the end of life.
They were discovered by French chemist Paul Villard (1860-1934).
While X-rays are produced by electronic transitions generally caused by the collision of an electron with an atom at high speed, gamma rays are produced by nuclear transitions.
Gamma rays produce damage similar to those produced by X-ray or ultraviolet (burns, cancer and genetic mutations).
Gamma-ray sources that we observe in the Universe come from massive stars (hypernova) who end their lives by a gravitational collapse leading to the formation of a neutron star or black hole.