Definition
All objects in nature, as long as the temperature in the absolute temperature above zero, are in the form of electromagnetic waves constantly transmit heat to the outside, this way of transmitting energy is called radiation. Objects through the radiation of the energy released, known as radiant energy, referred to as radiation.
Radiation has an important characteristic, that is, it is "reciprocal". No matter how high or low the temperature of the object (gas) are radiated outward, A object can be radiated to the B object, at the same time, B can also be radiated to A. This is different from conduction. This is different from conduction, which is unidirectional.
Radiation energy is absorbed by the body when the thermal effect occurs, the object absorbs different radiation energy, the resulting temperature is different. Therefore, radiation is an important way to convert energy into heat. Radiant heat transfer (radiant heat transfer) rely on electromagnetic radiation to realize the process of heat transfer between hot and cold objects, is a kind of non-contact heat transfer, can also be carried out in a vacuum. Electromagnetic waves emitted by the object, theoretically, is distributed throughout the spectral range, but in the temperature range encountered in industry, the practical significance of the wavelength is located between 0.38 ~ 1000μm thermal radiation, and most of them are located in the infrared (also known as heat rays) in the region of 0.76 ~ 20μm range. The so-called infrared heating, is the use of this section of thermal radiation. The study of the law of thermal radiation, for the reasonable design of the furnace heat transfer is very important, for high temperature furnace operator labor protection also has positive significance. When a system needs insulation, even if the temperature of this system is not high, the impact of radiation heat transfer can not be ignored. Such as silver-plated thermos bottle guts, is to reduce the heat loss caused by radiation heat transfer. The basic concept of thermal radiation any object in the emission of radiant energy at the same time, but also constantly absorbing the radiant energy sent by the surrounding objects. The difference between the energy radiated by an object and the energy absorbed is the net energy it transfers out. The radiative capacity of an object (i.e., the amount of energy radiated per unit of time per unit of surface) increases rapidly with increasing temperature. Generally speaking, when an object is subjected to other objects thrown radiation (energy Q), which is absorbed into the thermal energy of the part of the QA, is reflected part of the QR, through the object of the part of the QD, it is clear that these parts of the total energy and the relationship shown in the following formula: QA + QR + QD = Q If A = QA / Q is called the rate of absorption, R = QR / Q is called the rate of reflection, D = QD / Q If A=QA/Q is called the absorption rate, R=QR/Q is called the reflection rate, and D=QD/Q is called the penetration rate, then we have: A+R+D=1
If the object's A=1, R=D=0, i.e., the energy of the thermal radiation that arrives at the surface of the object is completely absorbed, the object is called an absolute blackbody, or blackbody for short. If R = 1, A = D = 0, that is, to reach the surface of the object of the thermal radiation of the energy is reflected; when this reflection is regular, this object is called a mirror body; if it is a chaotic reflection, it is called an absolute white body. If D = 1, A = R = 0, i.e., all the energy of the thermal radiation reaching the surface of the object is transmitted through the object, the object is called a heat-transmitting body. In fact, there is no absolute black body and absolute white body, only some objects close to the absolute black body or absolute white body. For example: no glossy black paint surface close to the black body, the absorption rate of 0.97 ~ 0.98; polished copper surface close to the white body, the reflectivity of up to 0.97. Affect the absorption and reflection of solid surfaces of the nature of the surface, mainly the surface condition and color, the surface condition of the impact is often greater than the color. Solids and liquids are generally impervious to heat. Thermal radiation energy through the surface of the solid or liquid after only a short distance (generally less than 1mm, through the metal surface after only 1μm), it is completely absorbed. Gases have little or no ability to reflect thermal radiation energy, monoatomic and symmetric diatomic gases (such as Ar, He, H2, N2, O2, etc.) at general temperatures can be regarded as heat-transparent, polyatomic gases (such as CO2, H2O, SO2, NH3, CH4, etc.) in a specific range of wavelengths has a considerable absorption capacity.
Radiation is dispersed outward in the form of electromagnetic waves. It is the propagation of energy in the form of fluctuations. Radio waves and light waves are electromagnetic waves. They travel very fast, the same speed as light waves (3 x 1010 cm/sec) in a vacuum and a little slower in air.
An electromagnetic wave is a synthetic wave composed of waves of different wavelengths. Its wavelength ranges from 10E-10 microns (1 micron = 10E-4 cm) of cosmic rays to radio waves with wavelengths up to several kilometers. Υ rays, X-rays, ultraviolet light, visible light, infrared light, ultrashort-wave and long-wave radio waves belong to the range of electromagnetic waves. What is visible to the naked eye is a very short section of electromagnetic waves, from 0.4-0.76 micrometers this part is called visible light. Visible light by the prism after spectroscopy, become a band of red, orange, yellow, green, cyan, blue, purple seven colors, which is called the light band spectrum. The longest wavelength of red light, violet wavelength is the shortest, the wavelength of the other colors of light is in between. Wavelength longer than red light (& gt; 0.76 microns) have infrared radio waves; wavelength shorter than the violet light (& lt; 0.4 microns) have ultraviolet, Υ rays, X-rays and so on. These radiations are invisible to the naked eye, but can be measured by instruments.
The wavelength of solar radiation is mainly 0.15-4 microns, of which the maximum radiation wavelength is 0.5 microns on average; ground and atmospheric radiation wavelength is mainly 3-120 microns, of which the maximum radiation wavelength is 10 microns on average. It is customary to refer to the former as short-wave radiation and the latter as long-wave radiation.
Hazards
People who work, study, and live in an environment where radiation sources are concentrated are prone to insomnia, memory loss, physical weakness, low immunity, etc., and the growth rate of their cancer cells is twenty-four times faster than that of normal people.
How far is radiation from us In our living environment, radiation is everywhere!
Household appliances: TV, refrigerator, air conditioning, microwave ovens, vacuum cleaners, etc.
Office equipment: cell phones, computers, copiers, electronic instruments, medical equipment, etc.
Home decoration: marble, laminate flooring, wallpaper, paint, etc.
Peripheral environment: high-voltage lines, power substations, television (radio) signal transmission towers,
Natural environment: sunspots, etc.
Because of the different resistance of each person's body, each person will have different degrees of symptoms. Generally polluted by electromagnetic radiation can cause headaches, insomnia, heart rate irregularities and other central nervous system problems. At the same time, for some people's eyes may have an impact, vision loss, skin diseases and other phenomena, heavy and may cause cancer. For pregnant women, it may lead to miscarriage, and elderly people with cardiac pacemakers should be especially careful. At the same time, different people or the same person at different ages on the tolerance of electromagnetic radiation is not the same, even in the excessive environment, does not mean that all people will get sick, so there is no need to electromagnetic radiation "grass". However, the elderly, children, pregnant women or patients with pacemakers, sensitive to electromagnetic radiation and long-term work in the environment of excessive dose of electromagnetic radiation should take precautions.
Prevention
With the rapid development of science and technology, a variety of scientific and technological products, household appliances into people's lives, all of which have greatly improved people's work efficiency, improve people's lives, do not dare to imagine that, if there is no such electrically charged equipment people's lives will be how? However, with the city around the high-voltage electricity, transmission towers are getting higher and higher, more and more electrical equipment at home, people feel convenient at the same time, but also in the harm. Electromagnetic radiation pollution has become the fourth largest environmental pollution after water, air and noise. If one day, you live in the house was suddenly told in the more serious electromagnetic radiation, how would you? Can you find out which of the many household appliances have higher levels of radiation? What is electromagnetic radiation? Professionally speaking, electromagnetic radiation is the phenomenon of energy traveling through space in the form of electromagnetic waves. Almost any electrical appliance in our home generates electromagnetic radiation. For example, microwave ovens, televisions, computers, cell phones and so on!
Protective clothing: including outerwear, vests, aprons, maternity clothes, etc., made of special fibers, has a better anti-electromagnetic radiation, anti-static effect. Especially families with microwave ovens, it is best to equip with protective aprons, which can effectively prevent electromagnetic radiation. For pregnant women if contact with electrical equipment, be sure to wear protective bibs or protective clothing to ensure the healthy growth of the fetus.
Anti-radiation screen: anti-radiation, anti-static, anti-glare and many other effects on the protection of eyesight also have a certain effect.
Another way is to pay attention to the time and distance.
The degree of damage is directly proportional to the time, that is, the longer the exposure to electromagnetic radiation, the greater the damage. And inversely proportional to the distance, the distance is ten times larger, the radiation is one percent of the original, the distance is one hundred times larger, the radiation is one millionth.
The difference between electromagnetic radiation and electromagnetic radiation pollution?
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 produce negative effects, causing different lesions and harm to the human body, this part of the radiation exceeds the standard electromagnetic field strength called electromagnetic radiation pollution.
What is the effect of cell phone base station radiation on the human body?
This is a relatively common phenomenon, in the city many residents upstairs are installed with cell phone base stations. Some members of the public are concerned about whether the electromagnetic radiation generated by such a device will be harmful to the human body. In fact, this problem, there is no need to worry. The difference between cell phone radiation and cell phone base station radiation. Generally a cell phone has an electromagnetic radiation value between 0.03-0.7, while a cell phone base station has a radiation value of 10 microwatts. The value of radiation produced by a cell phone base station is not much higher than the value of a cell phone!
In addition, electromagnetic radiation is the closer the distance, the longer the radiation exposure, the deeper the damage suffered! The cell phone base station installed on the roof of our general residential building is a safe distance away from us, so we can rest assured!
Specific electrical equipment protection at home is divided into:
A microwave
Alert index: ★★★★★
Microwave oven microwave has a thermal effect of this feature, to achieve the purpose of heating, cooking food. Studies have shown that microwave ovens produce strong electromagnetic waves that may induce disease by exceeding serious standards.
Response:
1, the microwave oven in the opening of the best left a meter or so.
2, often use microwave cooking food can wear shielding apron, shielding coat.
3, microwave ovens in the use of 6 to 7 years after the best out of the update.
Second, the computer
Alert index: ★★★★★
Response:
1, if you have to use the computer for a long time, you should pay attention to wash your face in time.
2, the use of computers should maintain a correct posture, the distance between the person and the computer screen is best to keep in more than 70CM.
3, the back and sides of the computer electromagnetic radiation intensity is no less than the intensity of the screen, it is best to keep more than 120CM.
4, LCD monitors are less harmful to the human body.
Third, the TV
Alert index: ★
Response:
1, the TV should not be set up with other appliances is too centralized, so that they are exposed to the risk of ultra-dose radiation.
2, the distance between the TV and people should be at least 2 meters away, should not be too close to the screen.
3, TV and other appliances are best not placed in the bedroom.
Also note that, for many people, lying in bed reading, reading the newspaper is a life interest. But like the radio, Walkman, cell phones and other small appliances are not suitable for the bedside, so as not to be subject to electromagnetic radiation.
Finally, if the long-term in the source of electromagnetic radiation, the body feels uncomfortable, should be as soon as possible to find the relevant departments to monitor, test, find the source of radiation. Avoid long-term damage.