Create a free Team What is Teams? Learn more. How far can radio waves travel in vacuum? Ask Question. Asked 2 years, 4 months ago.
Active 2 years, 4 months ago. Viewed 2k times. Improve this question. Cang Ye. Cang Ye Cang Ye 2 2 silver badges 8 8 bronze badges. Add a comment. Active Oldest Votes. Improve this answer.
Natsfan Natsfan 2, 2 2 gold badges 7 7 silver badges 12 12 bronze badges. Michael Walsby Michael Walsby 1, 3 3 silver badges 6 6 bronze badges. Einstein's Nobel Prize was for his paper on the photoelectric effect. If they couldn't do that, radios wouldn't work. The electromagnetic spectrum Type of wave Typical source Example of detector Approximate wavelength Typical users Dangers of over exposure Radio: LW electronic circuits, stars and space aerial and electronic circuit 1km communications, radio, TV safe unless very concentrated Radio: MW electronic circuits, stars and space aerial and electronic circuit m communications, radio, TV safe unless very concentrated Radio: VHF electronic circuits, stars and space aerial and electronic circuit 1m communications, radio, TV safe unless very concentrated Microwaves electronic circuits, cool objects aerial and electronic circuit 1cm 10 -2 m communications satellites, telephony, heating water and food burning, if concentrated Infra red IR electronic devices, warm objects, sun electronic detectors, special photographic film, blackened thermometer 0.
National 4 Subjects National 4 Subjects up. Radio: LW. 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. Gamma rays are produced by a number of astronomical processes in which very high-energy electrons are produced. Such electrons produce secondary gamma rays by the mechanisms of bremsstrahlung, inverse Compton scattering and synchrotron radiation.
Notable artificial sources of gamma rays include fission such as occurs in nuclear reactors, and high energy physics experiments, such as neutral pion decay and nuclear fusion. Gamma rays have characteristics identical to X-rays of the same frequency—they differ only in source. They have many of the same uses as X-rays, including cancer therapy.
Gamma radiation from radioactive materials is used in nuclear medicine. The distinction between X-rays and gamma rays has changed in recent decades. Originally, the electromagnetic radiation emitted by X-ray tubes almost invariably had a longer wavelength than the radiation gamma rays emitted by radioactive nuclei.
However, with artificial sources now able to duplicate any electromagnetic radiation that originates in the nucleus, as well as far higher energies, the wavelengths characteristic of radioactive gamma ray sources vs.
0コメント