When you tune in your radio, the dial number indicates the kilo or megaHertz at which the signal is being broadcast. Radio signal uses specific frequency, or how quickly the waves of the field move up and down. Hertz is a measurement of the number of wave cycles per second - AM is expressed in kiloHertz, while FM radio is expressed in megaHertz. The station power affects the range of the signal, or how far it can travel. He used a spark gap attached to an induction coil and a separate spark gap on a receiving antenna.
When waves created by the sparks of the coil transmitter were picked up by the receiving antenna, sparks would jump its gap as well.
Hertz showed in his experiments that these signals possessed all the properties of electromagnetic waves. You can tune a radio to a specific wavelength—or frequency—and listen to your favorite music. The radio "receives" these electromagnetic radio waves and converts them to mechanical vibrations in the speaker to create the sound waves you can hear. Astronomical objects that have a changing magnetic field can produce radio waves. Data pictured below show emissions from a variety of sources including radio bursts from the Sun, the Earth, and even from Jupiter's ionosphere whose wavelengths measure about fifteen meters in length.
Radio telescopes look toward the heavens to view planets, comets, giant clouds of gas and dust, stars, and galaxies. By studying the radio waves originating from these sources, astronomers can learn about their composition, structure, and motion. Radio astronomy has the advantage that sunlight, clouds, and rain do not affect observations.
Since radio waves are longer than optical waves, radio telescopes are made differently than the telescopes used for visible light. Radio telescopes must be physically larger than an optical telescopes in order to make images of comparable resolution. But they can be made lighter with millions of small holes cut through the dish since the long radio waves are too big to "see" them. The Parkes radio telescope, which has a dish 64 meters wide, cannot yield an image any clearer than a small backyard optical telescope!
In order to make a clearer, or higher resolution, radio image, radio astronomers often combine several smaller telescopes, or receiving dishes, into an array. Together, these dishes can act as one large telescope whose resolution is set by the maximum size of the area. The VLA consists of 27 antennas arranged in a huge "Y" pattern up to 36 km across roughly one-and-one-half times the size of Washington, DC.
The techniques used in radio astronomy at long wavelengths can sometimes be applied at the shorter end of the radio spectrum—the microwave portion.
Infrared radiation can be used to remotely determine the temperature of objects if the emissivity is known. This is termed thermography, mainly used in military and industrial applications but the technology is reaching the public market in the form of infrared cameras on cars due to the massively reduced production costs.
Applications of IR waves extend to heating, communication, meteorology, spectroscopy, astronomy, biological and medical science, and even the analysis of works of art. Visible light is the portion of the electromagnetic spectrum that is visible to the human eye, ranging from roughly to nm.
Visible light, as called the visible spectrum, is the portion of the electromagnetic spectrum that is visible to can be detected by the human eye. A typical human eye will respond to wavelengths from about to nm 0. In terms of frequency, this corresponds to a band in the vicinity of — THz. A light-adapted eye generally has its maximum sensitivity at around nm THz , in the green region of the optical spectrum.
The spectrum does not, however, contain all the colors that the human eyes and brain can distinguish. Unsaturated colors such as pink, or purple variations such as magenta, are absent, for example, because they can be made only by a mix of multiple wavelengths. Visible light is produced by vibrations and rotations of atoms and molecules, as well as by electronic transitions within atoms and molecules.
The receivers or detectors of light largely utilize electronic transitions. We say the atoms and molecules are excited when they absorb and relax when they emit through electronic transitions.
Visible Spectrum : A small part of the electromagnetic spectrum that includes its visible components. The divisions between infrared, visible, and ultraviolet are not perfectly distinct, nor are those between the seven rainbow colors.
The figure above shows this part of the spectrum, together with the colors associated with particular pure wavelengths. Red light has the lowest frequencies and longest wavelengths, while violet has the highest frequencies and shortest wavelengths. Blackbody radiation from the Sun peaks in the visible part of the spectrum but is more intense in the red than in the violet, making the Sun yellowish in appearance.
Colors that can be produced by visible light of a narrow band of wavelengths monochromaticlight are called pure spectral colors. Quantitatively, the regions of the visible spectrum encompassing each spectral color can be delineated roughly as:.
Note that each color can come in many shades, since the spectrum is continuous. The human eye is insensitive to electromagnetic radiation outside this range. By definition any images presented with data recorded from wavelengths other than those in the visible part of the spectrum such as IR images of humans or animals or astronomical X-ray images are necessarily in false color. An example of this phenomenon is that clean air scatters blue light more than red wavelengths, and so the midday sky appears blue.
The optical window is also called the visible window because it overlaps the human visible response spectrum. This allows visible light to heat the surface. The surface of the planet then emits energy primarily in infrared wavelengths, which has much greater difficulty escaping and thus causing the planet to cool due to the opacity of the atmosphere in the infrared.
Plants, like animals, have evolved to utilize and respond to parts of the electromagnetic spectrum they are embedded in. In plants, algae, and cyanobacteria, photosynthesis uses carbon dioxide and water, releasing oxygen as a waste product. Photosynthesis is vital for all aerobic life on Earth such as humans and animals. The portion of the EM spectrum used by photosynthesic organisms is called the photosynthetically active region PAR and corresponds to solar radiation between and nm, substantially overlapping with the range of human vision.
Ultraviolet UV light is electromagnetic radiation with a wavelength shorter than that of visible light in the range 10 nm to nm. It is so-named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the color violet. These frequencies are invisible to humans, but visible to a number of insects and birds. It can cause chemical reactions, and causes many substances to glow or fluoresce.
Most ultraviolet is classified as non-ionizing radiation. However, the entire spectrum of ultraviolet radiation has some of the biological features of ionizing radiation, in doing far more damage to many molecules in biological systems than is accounted for by simple heating effects an example is sunburn.
Although ultraviolet radiation is invisible to the human eye, most people are aware of the effects of UV on the skin, called suntan and sunburn. Much of it is near-ultraviolet that does not cause sunburn, but is still capable of causing long term skin damage and cancer.
An even smaller fraction of ultraviolet that reaches the ground is responsible for sunburn and also the formation of vitamin D peak production occurring between and nm in all organisms that make this vitamin including humans. The UV spectrum thus has many effects, both beneficial and damaging, to human health.
An overexposure to UVB radiation can cause sunburn and some forms of skin cancer. In humans, prolonged exposure to solar UV radiation may result in acute and chronic health effects on the skin, eye, and immune system.
Moreover, UVC can cause adverse effects that can variously be mutagenic or carcinogenic. The International Agency for Research on Cancer of the World Health Organization has classified all categories and wavelengths of ultraviolet radiation as a Group 1 carcinogen. UVB exposure induces the production of vitamin D in the skin. The majority of positive health effects are related to this vitamin.
It has regulatory roles in calcium metabolism which is vital for normal functioning of the nervous system, as well as for bone growth and maintenance of bone density , immunity, cell proliferation, insulin secretion, and blood pressure. X-rays are electromagnetic waves with wavelengths in the range of 0. They are shorter in wavelength than UV rays and longer than gamma rays. X-ray photons carry enough energy to ionize atoms and disrupt molecular bonds. This makes it a type of ionizing radiation and thereby harmful to living tissue.
A very high radiation dose over a short amount of time causes radiation sickness, while lower doses can give an increased risk of radiation-induced cancer. In medical imaging this increased cancer risk is generally greatly outweighed by the benefits of the examination. The ionizing capability of X-rays can be utilized in cancer treatment to kill malignant cells using radiation therapy. It is also used for material characterization using X-ray spectroscopy.
X-Ray Spectrum and Applications : X-rays are part of the electromagnetic spectrum, with wavelengths shorter than those of visible light. Different applications use different parts of the X-ray spectrum.
X-rays with photon energies above 5 to 10 keV below 0. Due to their penetrating ability, hard X-rays are widely used to image the inside of objects e. As a result, the term X-ray is metonymically used to refer to a radiographic image produced using this method, in addition to the method itself. Since the wavelength of hard X-rays are similar to the size of atoms, they are also useful for determining crystal structures by X-ray crystallography.
In medical diagnostic applications, the low energy soft X-rays are unwanted, since they are totally absorbed by the body, increasing the radiation dose without contributing to the image. Hence, a thin metal sheet, often of aluminum, called an X-ray filter, is usually placed over the window of the X-ray tube, absorbing the low energy part in the spectrum. This is called hardening the beam since it shifts the center of the spectrum towards higher energy or harder X-rays.
The distinction between X-rays and gamma rays is somewhat arbitrary. The electromagnetic radiation emitted by X-ray tubes generally has a longer wavelength than the radiation emitted by radioactive nuclei.
Historically, therefore, an alternative means of distinguishing between the two types of radiation has been by their origin: X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus. There is overlap between the wavelength bands of photons emitted by electrons outside the nucleus, and photons emitted by the nucleus.
Like all electromagnetic radiation, the properties of X-rays or gamma rays depend only on their wavelength and polarization. Gamma rays are very high frequency electromagnetic waves usually emitted from radioactive decay with frequencies greater than 10 19 Hz. Identify wavelength range characteristic for gamma rays, noting their biological effects and distinguishing them from gamma rays. However, this is not a hard and fast definition, but rather only a rule-of-thumb description for natural processes.
Gamma rays from radioactive decay are defined as gamma rays no matter what their energy, so that there is no lower limit to gamma energy derived from radioactive decay. Gamma decay commonly produces energies of a few hundred keV, and almost always less than 10 MeV. Gamma rays are ionizing radiation and are thus biologically hazardous. They are classically produced by the decay from high energy states of atomic nuclei, a process called gamma decay, but are also created by other processes.
Paul Villard, a French chemist and physicist, discovered gamma radiation in , while studying radiation emitted from radium during its gamma decay.
Natural sources of gamma rays on Earth include gamma decay from naturally occurring radioisotopes such as potassium, and also as a secondary radiation from various atmospheric interactions with cosmic ray particles. Some rare terrestrial natural sources that produce gamma rays that are not of a nuclear origin, are lightning strikes and terrestrial gamma-ray flashes, which produce high energy emissions from natural high-energy voltages.
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