This article mainly focuses on electromagnetic radiation and light in particular, and we will mainly consider the spectrum from UV light to infrared light. Electromagnetic radiation is the energy that has the properties of both waves and particles, known as wave-particle duality. Its wave component is a composite wave, consisting of the magnetic and the electric waves, which oscillate in space perpendicular to each other.
The particles that carry electromagnetic energy are called photons. They are more active at higher frequencies. The higher the frequencies and the smaller the wavelength , the more damage the photos can inflict on the cells of living organisms.
This is because the higher the frequency, the more energy the photons have and the more they can force the particles to change the molecular composition of tissue and other matter. In particular, ultraviolet, x-rays, and gamma radiation are especially harmful. Some of the cosmic electromagnetic radiation with high frequency is blocked by the ozone layer, but it is still present in the environment.
The atmosphere of the Earth allows only some electromagnetic radiation to pass through. Most of the gamma rays, x-rays, and ultraviolet light, as well as some infrared and some radio waves with long wavelengths, are blocked. More specifically, they are absorbed by the atmosphere. The rest of the radiation passes through the atmosphere. The UV light that does get through to the surface of the Earth causes skin damage sunburns and skin cancer.
On the other hand, the infrared light that passes through the atmosphere is useful to astronomers. They employ it in space observation when using infrared telescopes. The higher the altitude, the more infrared light can be found, thus many observatories that use infrared devices are built as high as possible, for example, in mountains. Some telescopes are sent above the atmosphere and into space, to allow for better infrared radiation detection.
Wavelength and frequency are inversely proportional. This means that as the wavelength increases, the frequency decreases, and conversely, the lower the wavelength — the higher the frequency. This makes sense, because if the wave oscillates a lot its frequency is high , there have to be more peaks per a given time period, and thus the time between the waves must be shorter.
When the frequency is multiplied by the wavelength, it yields the speed of the wave. Electromagnetic waves always move at the same speed in a vacuum, known as the speed of light. It equals ,, meters per second. Light is an electromagnetic wave, and as such has frequency and wavelength.
The shortest wavelength for visible light is nanometers for violet light, and the spectrum continues to indigo and blue, then to green and yellow, orange, and finally — red. One can split the visible light into its components by using a prism. This is possible because the wavelengths for each color are different, and when light bends inside the prism, it comes out at different angles, depending on this wavelength.
This phenomenon is called dispersion. The regular white light projects an image of colors in the same sequence as they appear in the rainbow. A rainbow is formed similarly. Here droplets of water act in the same way as a prism, making the light split into its component waves. The colors of the rainbow have played such an important role throughout human culture and we use them so often on the daily basis, that there are mnemonics in many languages to teach the colors of the rainbow to children from an early age.
For example, in English, there are several songs about a fictional character, Roy G. Each letter of his name stands for the first letter of a color in the rainbow, red, orange, yellow, green, blue, indigo, and violet. The letters in his name are in sequence. The human eye is the most sensitive to light with a wavelength of nm when the light is bright, and nm in low light. Not all animals are sensitive enough to color light to be able to differentiate all the colors, however.
For example, cats do not have color vision. On the other hand, some animals are much better at differentiating colors than humans are, and they can even see ultraviolet and infrared light. For an object to have a specific color means that light of a particular wavelength is reflected from or emitted by this object. Objects that appear white reflect all the colors, while objects that we see as black absorb all the colors and reflect nothing back.
A diamond is an example of an object that has very high dispersion. A diamond that is cut well is similar to a prism. The light enters the diamond and reflects from its many sides and comes out again. This makes it sparkle brilliantly. Its cut is very important, however.
With a correctly-cut diamond, the light will come inside, reflect off the sides once or twice, and then come out from the top again, where we can see it, as shown in the diagram.
Spectral analysis or spectroscopy is used to understand the chemical composition of objects. This is especially useful when a direct chemical analysis is impossible, such as with stars. A branch of spectroscopy called absorption spectroscopy measures what type of radiation the object absorbs. The chemical structure of the materials determines what kind of light it will absorb, based on the wavelengths.
This is a useful tool in analyzing what materials the object is made from. It is possible to complete this analysis at a distance, which is beneficial not only in astronomy, but also when dealing with hazardous, fragile, or very small objects. Electromagnetic radiation is energy, and so is light, so its detection is dependent on the amount of energy emitted.
The longer the wavelength, the less energy is emitted. The ability of animals to detect this energy and their sensitivity to specific amounts of energy is what makes vision a reality.
This ability allows animals to differentiate between different types of electromagnetic radiation, in particular for visible light — colors. The ability of man-made technology to detect this radiation is built on the same principles.
Animals and humans can detect a range of electromagnetic energy. Many animals, including humans, detect visible light in some form. In some cases this allows animals to see a range of colors, but in other cases, they can only see the difference between light and dark areas. The photons enter the eye through the retina and are absorbed by the chemical components inside the vision receptors, called cones.
The eye has another type of photoreceptors called rods, but they cannot differentiate colors. Instead, they determine how strong the light is. There are usually different types of cones in the eye. Humans have three types of cones. They absorb photons with specific ranges of wavelengths, which correspond to visible light of a range of given colors.
This triggers a chemical reaction, which, in turn, sends a neural signal through the nervous system to the visual cortex in the brain, the area that processes color information. The combination of information about how much each type of cones was stimulated is then used to determine which color is seen. While humans have 3 types of cones, some other animals such as some species of birds and fish have 4 and 5 types of cones.
It is interesting that in some species females have more types of cones than do males. Gulls that feed at the surface or plunge for food, as well as many other birds, have red or yellow oil droplets in the cones of their retinas. This oil acts as a filter and allows birds to see more colors. Reptiles also have this feature. Snakes have not only visual receptors but also a sensor that can detect infrared light. Their sensors absorb the energy, emitted by infrared light in the form of heat.
Infrared can also be detected as heat by special devices such as infrared goggles — a technology used in combat and security.
Some bats can see infrared light also, and so can some insects. Animals and devices that can track light using temperature can usually see if the area has been disturbed recently, for example, if a rodent dug a hole in the earth or if a criminal hid something in the ground. Infrared is used in telescopes as well to detect distant astronomical bodies.
Other uses for infrared radiation include determining temperature changes, for example, while checking for temperature leaks, in security, in art history, in meteorology, in medicine, and many other fields. Unlike humans, some fish can detect ultraviolet light by absorbing it.
Their visual system contains pigment that is sensitive to UV. It is believed that this ability is useful for feeding behaviors and choosing mates, as well as for some other social behaviors. Some birds also detect ultraviolet light, and similar to fish this ability is commonly used in courtship, to distinguish a potential mate.
Some plant and animal material reflects UV light well, and these birds use their sensitivity to harvest food. Several species of lizards, turtles, and rodents also have this ability. Green iguana species pictured are one example. Human eyes can absorb UV as well, but it is not detected. Instead extended exposure damages cells in the retina, the cornea, and the lens, and can cause a range of eye diseases, as well as blindness.
Similar to infrared light, UV is used in a range of areas such as medicine, disinfection, curing materials, chemical imaging, in space observatories, to detect forged currency and sometimes IDs if they are supposed to have marks printed in special UV-detectable ink.
The latter does not always work, because some fake IDs are made from real IDs, but the photograph or other information is substituted. In this case, they would have the special UV-detectable marks, just like the real IDs. Small amounts of UV are also needed by humans and some animals to produce vitamin D. UV radiation is used in other fields as well. Defects in color vision sometimes cause the inability to distinguish between colors.
This could be manifested for a particular wavelength or for all colors. Often this is caused by damaged or underdeveloped photoreceptors, but it could also be caused by the problems higher along the neural pathway to the brain, including brain damage in the visual cortex where the color information is processed.
In most cases, this condition provides a disadvantage, but since many animals are color-blind, some scientists believe that this is a trait that developed through natural selection and gave an evolutionary advantage to some species. For example, color-blind animals and people can see camouflaged animals better than those, who have color vision intact.
Despite the potential benefits, color-blindness is viewed as a disadvantage in human society, and some vocational opportunities are limited only to people with normal color vision. Some countries restrict or completely revoke driving privileges for color-blind people, and it is generally not possible to get a full, restriction-free piloting license for them.
Jobs that rely on color information, such as graphic design or professions in which color serves as a warning or as a direction are generally not available to people with color-blindness.
To address the problem of color-blindness in people a range of tools is being developed, such as color code tables that use signs to represent colors. These signs are sometimes used together with color-coding in public places by several countries. Some graphic designers choose not to use color-coding all together or prefer a combination of color and other visual information such as brightness , to ensure that even the color-blind persons benefit from the design. Some computer interfaces also accommodate for color-blindness under the accessibility settings.
Computer vision is a rapidly developing field of artificial intelligence and color recognition is one of its branches. Until recently a considerable amount of research and development in computer vision has been done without color, but more labs are working on incorporating color vision into their projects.
Note: Nanohertz is a metric unit of frequency. Terahertz is a metric unit of frequency. List of these foods starting with the highest contents of Cysteine and the lowest contents of Cysteine.
Calculate how much of this gravel is required to attain a specific depth in a cylindrical , quarter cylindrical or in a rectangular shaped aquarium or pond [ weight to volume volume to weight price ].
Volume to weight , weight to volume and cost conversions for Refrigerant RB, liquid RB with temperature in the range of The grain per liter density measurement unit is used to measure volume in liters in order to estimate weight or mass in grains The online number conversions include conversions between binary, octal, decimal and hexadecimal numbers.
0コメント