Radiation has an important feature that it is "equivalent". No matter the temperature of the object (gas) is high or low, it radiates outward. Object A can radiate to object B, and at the same time, object B can also radiate to object A.. This is different from conduction, which is unidirectional. People exposed to a lot of radiation should wash their whole bodies thoroughly with soap and plenty of water, and seek the help of doctors or experts immediately! (The picture shows the warning sign of "Danger of radioactive materials, be careful of radiation")
When radiant energy is absorbed by an object, thermal effect occurs. Different radiant energy absorbed by the object leads to different temperatures. Therefore, radiation is an important way to convert energy into heat. Radiant heat transfer is a process of heat transfer between hot and cold objects by electromagnetic radiation, which is a non-contact heat transfer and can also be carried out in vacuum. The electromagnetic waves emitted by objects are theoretically distributed in the whole spectrum range, but in the temperature range encountered in industry, the practical significance is the thermal radiation with the wavelength of .38 ~ 1 μ m, and most of them are in the range of .76 ~ 2 μ m in the infrared (also known as thermal radiation) section. The so-called infrared heating is to use the thermal radiation of this section. It is very important to study the law of thermal radiation for the reasonable design of heat transfer in the furnace, and it is also of positive significance for the labor protection of operators in high temperature furnaces. When a system needs heat preservation, even if the temperature of the system is not high, the influence of radiation heat transfer can not be ignored. For example, the silver plating of thermos bottles is to reduce the heat loss caused by radiation heat transfer. The basic concept of thermal radiation Any object emits radiant energy, at the same time, it constantly absorbs the radiant energy from the surrounding objects. The difference between the energy radiated by an object and the energy absorbed is the net energy it transmits. The radiation ability of an object (that is, the energy radiated from the surface per unit time) increases rapidly with the increase of temperature. Generally speaking, when an object is radiated by other objects (energy is Q), the part that is absorbed and converted into heat energy is QA, the part that is reflected is QR, and the part that passes through the object is QD. Obviously, there is a relationship between these parts and the total energy: QA+QR+QD=Q If A=QA/Q is called absorption rate, R=QR/Q is called reflectivity, and D = QD. Then there is: A+R+D=1 radiation
if A=1 and R=D= of an object, that is, the energy of thermal radiation reaching the surface of the object is completely absorbed, and this object is called an absolute blackbody, which is called blackbody for short. If R=1 and A=D=, that is, all the energy of thermal radiation reaching the surface of the object is reflected; When this reflection is regular, this object is called a mirror; If it is a random reflection, it is called an absolute white body. If D=1 and A=R=, that is, all the energy of thermal radiation reaching the surface of the object passes through the object, which is called a diatherm. In fact, there is no absolute blackbody or absolute white body, only some objects are close to absolute blackbody or absolute white body. For example, the surface of dull black paint is close to blackbody, and its absorption rate is .97 ~ .98; The polished copper surface is close to the white body, and its reflectivity can reach .97. The absorption and reflection properties of solid surface are mainly influenced by surface condition and color, and the influence of surface condition is often greater than color. Solids and liquids are generally impervious to heat. The energy of thermal radiation is completely absorbed only after passing through the surface of solid or liquid for a short distance (generally less than 1mm, and only after passing through the metal surface for 1μm). Gases have almost no ability to reflect thermal radiation energy. Monoatomic and symmetric diatomic gases (such as Ar, He, H2, N2, O2, etc.) at general temperature can be regarded as diatherms, while polyatomic gases (such as CO2, H2O, SO2, NH3, CH4, etc.) have considerable absorption ability in a specific wavelength range.
radiation is emitted in the form of electromagnetic waves and particles (such as alpha particles and beta particles). Radio waves and light waves are electromagnetic waves. Their propagation speed is very fast, which is the same as that of light wave (3×11 cm/s) in vacuum, but slightly slower in air.
electromagnetic wave is a composite wave composed of waves with different wavelengths. Its wavelength ranges from cosmic rays of 1E-1 microns (1 micron =1E-4 cm) to radio waves with a wave length of several kilometers. X-ray, X-ray, ultraviolet ray, visible light, infrared ray, ultrashort wave and long wave radio waves all belong to the range of electromagnetic waves. Visible to the naked eye is a very short section of electromagnetic wave, which is called visible light from .4-.76 micron. After the visible light is split by a prism, it becomes a light band composed of seven colors: red, orange, yellow, green, cyan, blue and purple. This light band is called spectrum. Among them, the wavelength of red light is the longest, the wavelength of purple light is the shortest, and the wavelengths of other colors of light are in between in turn. Wavelength longer than red light (>: .76 micron) has infrared rays and radio waves; Wavelength shorter than purple light (<: .4 micron) has ultraviolet rays, gamma rays, x rays, etc. Although these radiations are invisible to the naked eye, they can be measured by instruments.
the wavelength of solar radiation is mainly .15-4 microns, and the maximum radiation wavelength is .5 microns on average; The radiation wavelength of the ground and atmosphere is mainly 3-12 microns, and the maximum radiation wavelength is 1 microns on average. It is customary to call the former short-wave radiation and the latter long-wave radiation.
[ Edit this paragraph] Harm
People who work, study and live in an environment with concentrated radiation sources are prone to insomnia and dreaminess, memory loss, physical weakness and low immunity, and their cancer cells grow 24 times faster than normal people.
How far is radiation from us? In our living environment, radiation is everywhere!
Household appliances: TV, refrigerator, air conditioner, microwave oven, vacuum cleaner, etc.
Office equipment: mobile phone, computer, copier, electronic instrument, medical equipment, etc.
Home decoration: marble, composite floor, wall wallpaper, paint, etc.
Surrounding environment: high-voltage lines, substations, Television (radio) signal towers and other
natural environment: sunspots and other
A healthy person can resist a short-term load of 5, r, but only a dose of 7R is enough to make a healthy person fatally threatened, but everyone's physical resistance is different, and everyone will have different degrees of symptoms. Generally, being polluted by electromagnetic radiation will cause central nervous system problems such as headache, insomnia and arrhythmia. At the same time, it may have an impact on some people's eyes, such as decreased vision, skin diseases, and even cancer. For pregnant women who may cause miscarriage, elderly people who have installed cardiac pacemakers should pay special attention. At the same time, different people or the same person have different tolerance to electromagnetic radiation at different ages. Even in the environment exceeding the standard, it does not mean that everyone will get sick, so it is unnecessary to "be a soldier" for electromagnetic radiation. However, preventive measures should be taken for the elderly, children, pregnant women or patients with pacemakers, people who are sensitive to electromagnetic radiation and those who have worked in an environment of excessive electromagnetic radiation for a long time.
[ Edit this paragraph] Prevention
With the rapid development of science and technology, a variety of scientific and technological products and household appliances have entered people's lives, all of which have greatly improved people's work efficiency and improved people's lives. I dare not imagine what people's lives would be like without these live equipment. However, with the increasing high-voltage electricity and transmission towers around the city, there are more and more electrical equipment at home, which makes people feel convenient and hurt at the same time. At present, electromagnetic radiation pollution has become the fourth largest environmental pollution after water, air and noise. If one day, the house you live in is suddenly told that it is in serious electromagnetic radiation, what will you do? Among these many household appliances, can you find out which ones have higher radiation? What is electromagnetic radiation? From a professional point of view, electromagnetic radiation is the phenomenon that energy propagates through space in the form of electromagnetic waves. Almost any electrical appliance in our home will produce electromagnetic radiation. Such as microwave ovens, televisions, computers, mobile phones and so on! Radiation
protective clothing: including coats, vests, aprons, maternity clothes, etc., made of special fibers, which has good anti-electromagnetic radiation and anti-static effects. Especially for families with microwave ovens, it is best to equip them with protective aprons, which can effectively prevent electromagnetic radiation. For pregnant women, if they come into contact with electrical equipment, they must wear protective Chinese-style chest covering or protective clothing to ensure the healthy growth of the fetus.
radiation shield: it has many functions, such as radiation protection, anti-static, anti-glare and so on, and also has a certain effect on protecting eyesight.
Another way is to pay attention to the time and distance or eye drops.
the degree of injury is proportional to time, that is, the longer the exposure to electromagnetic radiation, the greater the injury. And is proportional to the distance, the distance is ten times larger, the radiation is one percent of the original, and the distance is one hundred times larger, and the radiation is one ten thousandth.
[ Edit this paragraph] Q&A
A: What's the difference between electromagnetic radiation and electromagnetic radiation pollution?
Q: In fact, electromagnetic radiation and electromagnetic radiation pollution are two concepts. Any charged body has electromagnetic radiation. When the intensity of electromagnetic radiation exceeds the national standard, it will have negative effects and cause different diseases and harms to the human body. This part of radiation exceeding the standard electromagnetic field intensity is called electromagnetic radiation pollution.
A: what effect does the radiation from mobile phone base stations have on people's health?
Q: This is a common phenomenon. Many residential buildings in urban areas are equipped with mobile phone base stations. Some citizens are worried about whether the electromagnetic radiation generated by such a device will do harm to the human body. In fact, there is no need to worry about this issue. The difference between cell phone radiation and cell phone base station radiation. Generally, the electromagnetic radiation value of a mobile phone is between .3 and .7, while the radiation value of a mobile phone base station is 1 microwatts. The radiation value produced by a mobile phone base station is not much higher than that of a mobile phone! In addition, the closer the electromagnetic radiation is, the longer the radiation time is, the deeper the damage is! And the distance between the mobile phone base station installed on the roof of our general residents' house and us is a safe distance, so everyone can rest assured!
[ Edit this paragraph] The specific protection score of electrical equipment in the home
Electrical radiation index
The electrical radiation index is implemented on a five-point scale. Anyone who is rated as five points is seriously exceeding the standard, which should arouse your attention; Samsung and above also belong to the scope of exceeding the standard, which should also attract your attention; One-star, it is safe, you can rest assured to use it.
There are two levels of electromagnetic radiation, in which the unit of power frequency band is μT. If the radiation is above .4μT, it is strong radiation, which is harmful to human body and prone to leukemia after long-term contact. If the radiation is below .4μT, it is relatively safe. The unit of radio frequency electromagnetic wave is μW/㎝2.
1. TV
The traditional picture tube TV CRT was the first to be tested. First, we tested it at close range. In the front half meter, at the moment of normal startup, the radiation value it produced was .12μT, .3μT during normal viewing, .27μT during channel changing and .11μT in standby state, while the radiation value on the side was .28μT during normal viewing, which was close to the warning value on the whole.
because most people watch TV at a distance of about 3 meters, we have also done a test at the front 3 meters, and found that the radiation has a great degree of attenuation: the power on/off, normal viewing, channel changing and standby state are all .12μT, and the test results show that the normal viewing of traditional CRT TV will not cause harm. But to our surprise, the radiation intensity behind it is relatively high, and the radiation value reaches 4.8μT within half a meter after starting the machine, and the radiation has not decreased through the glass and wooden board, and even the radiation value is .9μT through the 1 cm thick wall. Be careful if the back of your TV is facing the bedside of your bedroom. But usually people have different time to rest and watch TV, so it's not a big problem.
looking at the plasma TV again, half a meter from the front, it is .11μT for turning on, watching and changing channels, .12μT for standby and .11μ t for side; At the front 3 meters, it is .12μT when turning on, .14μT when watching normally, and .11μT when changing channels and waiting. From the test results, the radiation intensity of plasma is smaller than that of traditional TV.
The rear projection TV, when viewed normally, is .12μT close to the front, .19μT to the side and .14 μ t to the back of the fuselage; .11μ t at the front half meter; .1μT at 3m from the front.
The most reassuring thing in TV series is LCD TV. No matter whether it is within half a meter of the front or 3 meters of the front, the test results at the moment of starting, normal viewing, channel changing and standby state are all .1μT, while the side is only .11μT, basically, the radiation intensity has not changed.
test results: after comparing the three TVs, we can easily find that LCD TV and rear projection TV have the smallest radiation, plasma TV has a little stronger radiation, and CRT TV is larger, but it is mainly behind the TV, suggesting that you'd better keep a certain distance when watching, especially for children.
2. DVD player and home theater
The popular home theater in recent years, that is, DVD player plus sound system, is close to the test results. The DVD player is 1.2μT, the OK player is 1.2 μ t, the power amplifier is 1.24μT, the small speaker is 1.5μT and the large speaker is .49 μ t. If it is turned on at the same time, the radiation is not small.
tip: I suggest you use the home theater as little as possible. If you want to sing, you'd better go to KTV.
CRT monitors, LCD monitors, desktop computers, mainframe computers, small speakers, notebook computers
People always think that CRT monitors emit a lot of radiation. Is it what everyone thinks? We first tested it, and the front of the display screen is close to 1.μT, and the side of the display screen is close to .55μT, which is not small! Looking at the center of the display screen, the distance is .3 meters, and the radiation is still .55 μ t. Is this CRT monitor really as big as we thought? In order to further confirm, we began to look for its safe distance. As a result, when the distance is .2 meters, the radiation in front of the display screen will be attenuated to .18 μ t. It seems that CRT monitors can be safely used as long as the distance is .2 meters. Some viewers asked if it was as big as CRT TV, but it was not big after the test. Some people like to use radiation-proof screensavers, so does it work? We also specially tested it, and the screensaver radiation is only reduced by 1%, so it seems that the screensaver has little effect.
radiation index of CRT monitor: ★★★☆☆
Now LCD monitor is replacing traditional monitor, and we have also tested it. .11μT in front of the display screen, .12μT in the instant of startup, .11μT in shutdown and .5 m .12μT in the side of the display screen. It seems that the LCD is really reassuring.