In ancient times, when productivity was underdeveloped, myth was the explanation of human nature. Of course, this is sometimes unscientific.
In fact, lightning is a form of electric current. When cold air meets warm and humid air, warm air rises rapidly to form rain clouds. When there is a storm, raindrops and ice crystals collide and rub against each other, resulting in a strong airflow, which increases the electrostatic charge in the cloud. At this time, the positive charge in the cloud is concentrated in the upper part of the cloud, and the negative charge is concentrated in the lower part of the cloud. When the negative charge at the bottom of the cloud reaches a certain level, it will release electricity and spread to the other end through the air. This energy release can be transferred from clouds to the ground or between clouds. Lightning will also heat the air, make it expand rapidly and make a huge noise, thus forming lightning.
When lightning occurs, the voltage can be as high as several hundred thousand volts, the lightning center temperature can be as high as 17000℃ ~ 25000℃, and several million to several hundred million joules of energy can be released within110 second.
Due to uneven air density and uneven resistance, the shape of lightning is mostly tortuous, forming a tree-like light band. There are many forms of lightning, such as linear, ribbon, spherical, string, arrow lightning and so on. A long-distance lightning will fall to the ground after about 50 laps, so the curved path of lightning is erratic. The colors of lightning are also varied, the most common ones are red, orange and yellow.
The speed of sound in the air is 340m/s, and the speed of light in the air is about 3x 108m/s ... radius of the earth is about 6,400km, and light can run around the earth seven and a half times a second! In The Journey to the West, Wu Cheng'en described the Monkey King's walking and somersaulting. If it takes one second for the Monkey King to do a somersault, the speed of the Monkey King is 5.4× 105 m/s, which is faster than thunder, but much slower than lightning.
Because lightning is much faster than thunder, people always see lightning first and then hear thunder. Therefore, according to the different speeds of lightning and thunder, people can calculate the distance between people and the place where lightning strikes. Because lightning happens at the same time, we can calculate the distance from seeing lightning to hearing it. If lightning is in the northwest, thunder is heard every 10 second, because lightning is very fast, its movement time is very small compared with thunder and can be ignored. If the time of thunder is 10 second, it can be calculated that the lightning is about 3400 meters away from us.
Electromagnetic measurement
Electromagnetic measurement includes the measurement of all electromagnetic quantities and other related quantities (frequency and phase angle of alternating current, etc.). Various special instruments (ammeter, voltmeter, ohmmeter, magnetic field meter, etc.). ) and measuring circuit, which can meet the measurement of various electromagnetic quantities. Another important aspect of electromagnetic measurement is the electrical measurement of non-electric quantities (length, speed, deformation, force, temperature, light intensity, composition, etc.). Its main principle is to use some effect of the correlation between electromagnetic quantity and non-electric quantity to transform the measurement of non-electric quantity into the measurement of electromagnetic quantity.