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Gas-discharge tubes and fluorescent lights

The electric discharge in rarefied gases. Gas-discharge tubes and fluorescent lights.

From a comparison of formulas WTo≥ AAnd and WTo=Ееλ (mυ2= Ееλ) see, when independent gas conductivity should be performed the ratio:

Ееλ≥ AAnd, (20.4)

t. e. if you increase the mean free path of electrons can be obtained independent conductivity gas at a lower field strength E, t. e. at a lower voltage. Thus, vacuum gas the conductivity should increase. This conclusion is confirmed by the following experience.

заряд в газах

We take a glass tube with two soldered electrodes and a hole for pumping air (rice. 20.5). Then the electrodes are connected across the voltage source of several thousand volts. If now through the hole And to drain from the tube to the air pump, then for sufficiently small the pressure of the air in the tube begins to glow. This means, what in the air have any self-discharge. Free electrons in the tube appear due to secondary emission at the cathode, on the surface of which ions collide.

Glow air varies with the degree of dilution of the. First, between the electrodes appear purple cords, and then lights up all the air in the tube pinkish light. Filling the tube with various gases and passing through them a current of, you can see, each gas (sparse) has its own color of light. For example, argon glows blue, neon — red and t. d.

схема включения лампы

Discharge in rarefied gas, accompanied by glow, call glow. Glow discharge emits are not particularly bright glow. The release of thermal energy in the gas gap when a glow discharge is insignificant, and the glowing gas is still cold. Glow discharge is used for the device gas-discharge tubes, which are widely used in light commercials.

Of lighting often use fluorescent lights, representing gas-discharge tubes, the walls are covered with a special composition — phosphor. The phosphor glows under the action of radiation of rarefied gas, occurs during the passage of current in the lamp. The phosphor absorbs mainly invisible radiation, and itself emits light radiation, the composition is close to visible radiation from the Sun. Inside the fluorescent lights are sparse inert gas and mercury vapor. The circuit of the lamp shown in figure. 20.6.

If you close the chain, the current goes through the starter and nakalyaet electrodes inside the lamp, from which thermionic emission occurs. Thus in the lamp begins to self discharge and high temperature of the electrodes is supported by the current in the lamp, and the starter is automatically disconnected.

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