How does the crackling sound of mosquito killing pats come out? It's the sound of electric arc generated by voltage breaking through air. Generally speaking, the mosquito killing racket will have three layers of metal nets, of which the outer two layers of sparse metal nets are the same pole, the middle one is the other pole. When the mosquito is between the inner and outer metal nets, the two poles discharge and electrocute the mosquito.

　　The voltage of the mosquito killing racket is very high. It should have thousands of volts. (Because the discharge is very small, it generally does not harm people, but it is enough to kill mosquitoes and flies.) The distance between the internal and external network is about 5 mm. At this time, the voltage is not enough to break down the air between the two poles. The two poles can be considered as insulating. Therefore, no discharge will occur at any time. When the mosquito enters the network between two layers, it can almost be regarded as a conductor because of its good electrical conductivity. At this time, the air layer between the two electrodes becomes thinner. When it is thin to a certain extent, the voltage breaks down the air and forms an arc discharge. Breakdown means that air molecules are ionized in an extremely strong electric field. What happens when air is ionized? Nitrogen and oxygen molecules in the air are electrically neutral. Under the electric field, the positive charge center and the negative charge center of the molecule are separated. The stronger the electric field, the more significant the separation is. Until the external electric field is strong enough that the electron can be completely separated from the Coulomb attraction of the atomic solid. At this point, the molecules no longer exist, only free electrons and ions. (The breakdown field of air is about 30 kV/cm. If the polar voltage of the mosquito killing racket is 3 KV, it can be ionized when the thickness of the air layer is about 1 mm.) This is when air conducts electricity.

　　The mosquito killing racket discharged through the road of "outer Net - mosquito body - ionized air - Inner net". The process of discharging ionized air is called arc. The sounds and sparks of mosquito killing pats are produced in this process. It's the same as thunder and lightning. This discharge process lasts only a short time. But the instantaneous temperature of the arc produced by air ionization can reach 5000 degrees Celsius. Intense thermal expansion and cold contraction rapidly promote the surrounding air. The speed of propulsion is faster than that of sound, in which the air collides violently with the air. That's why a little air can make such a loud crackle.