Briefly describe the working principle of fluorescent lamp, what is the working principle of fluores

There is a detailed explanation in the physics book for the third year of junior high school.

Structure and function of fluorescent lamp: there is a filament at each end of the fluorescent lamp, the lamp is filled with a trace amount of argon and thin mercury vapor, the inner wall of the lamp is coated with phosphor, and the gas between the two filaments emits ultraviolet rays when conductive, so that the phosphor emits soft visible light.

Working characteristics of fluorescent lamp: a high voltage is required when the lamp starts to ignite, and only a small current is allowed to pass through when the light is emitted normally, and the voltage at both ends of the lamp is lower than the power supply voltage.

The fluorescent tube is equipped with filament at both ends, and the inner wall of the glass tube is coated with a thin and uniform layer of phosphor, which is pumped into a vacuum of 10-3-10-4 mm Hg, filled with a small amount of inert gas, and injected with a trace amount of liquid mercury. Inductive ballast is an iron core inductance coil, the nature of the inductance is that when the current in the coil changes, the ** circle will cause a change in magnetic flux, resulting in an induced electromotive force, which is in the opposite direction to the direction of the current, thus hindering the current change.

The emitter plays a switching role in the circuit, which is formed by a neon discharge tube and a capacitor in parallel, and the role of the capacitor is to eliminate the electromagnetic interference of the power supply and form an oscillation circuit with the ballast to increase the amplitude of the starting pulse voltage. One of the electrodes in the discharge tube is composed of a bimetal sheet, which is heated by neon bubble discharge, so that when the bimetal sheet is opened and closed, the current of the inductance ballast is abruptly changed and a high-voltage pulse is generated and added to both ends of the lamp.

After the fluorescent lamp is connected to the circuit, the glow discharge begins between the two electrodes of the igniter, so that the bimetal sheet is heated and expands and contacts with the static contact pole, so the power supply, the ballast, the filament and the radiator form a closed loop, the current preheats the filament, when the heating time is 1-3 seconds, the glow discharge between the two electrodes of the ignitor is extinguished, and then the bimetal sheet is cooled and disconnected from the static contact pole, when the two electrodes are disconnected, the current in the circuit suddenly disappears, so the ballast produces a high-voltage pulse, which is superimposed with the power supply. It is added to both ends of the lamp to ionize the inert gas in the lamp and cause arc discharge, and the self-inductance of the ballast also plays a role in stabilizing the current in the circuit during the normal luminescence process.

Something else I don't understand is asking me.

Principle: When the switch K is turned on, the power supply live wire supplies power to the fluorescent lamp through the fuse, switch and ballast, and at this time, a 220V voltage is applied at both ends of the fluorescent tube and the starter, so that the starter produces glow discharge.

The heat of the glow discharge makes the bimetal sheet expand by heating, so that the moving contact and the static contact are connected, and the current flows through the filament in the ballast coil and the lamp, and the filament is quickly heated by the current and emits a large number of electrons, at this time, the glow discharge of the starter disappears, and the temperature in the tube decreases; The bimetal sheet automatically resets, and the poles are disconnected.

At the moment when the two poles are disconnected, the circuit current is suddenly cut off, and the ballast produces a large self-induced electromotive force, which acts on both ends of the tube after superimposing the power supply voltage, and under the action of high voltage at both ends of the lamp, it moves from the low potential end to the high potential end at a great speed, collides with the argon molecules in the tube, makes it ionized rapidly, argon ionizes heat, and the heat makes the mercury produce vapor, and then the mercury vapor is also ionized, and emits strong ultraviolet light, under the excitation of ultraviolet rays, the phosphor in the tube wall emits almost white visible light.

After the fluorescent lamp glows normally. As the alternating current is constantly passing through the coil of the ballast, a self-induced electromotive force is generated in the coil, and the self-induced electromotive force hinders the current change in the coil. The ballast plays the role of step-down and current limiting, so that the current is stabilized within the rated current range of the lamp, and the voltage at both ends of the lamp is also stabilized within the rated working voltage range.

Since this voltage is lower than the ionization voltage of the starter, the starter connected in parallel at both ends no longer works.

The ballast generates instantaneous high pressure when starting, and plays the role of voltage reduction and current limiting during normal operation; The function of the capacitor in the starter is to avoid generating electrical sparks.