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Question

What are the one main components of a cathode ray tube ?

A
electron gun
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B
cathode tube
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C
U-tube
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D
none of these
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Solution

The correct option is A electron gun
The three main components of cathode ray tube are
1. elecron gun
The electron gun has a tungsten filament, two batteries, one low tension and one high tension, a switch, variable resistance, cathode plate, control grid, and double anode cylinders.
When the switch is in the ON position, direct current passes through the tungsten filament which is kept in series with the variable resistance. As the strength of the current is increased, the temperature of the filament increases. The strength of the current in the series circuit is adjusted using the variable resistance. The tungsten filament turns red hot and maintains the required steady temperature. The heat generated by the red hot tungsten filament is transferred to the cathode plate. As the cathode plate is coated with oxides of barium or strontium, it starts emitting thermions on getting heated up.
The number of thermions generated depends on the temperature of the cathode plate, which in turn is dependent upon the temperature of the tungsten filament. These thermions get attracted by the anode. They accelerate due to the high potential difference between the cathode and the anode. In between the cathode and anode there is control grid. This control grid is made of extremely fine wire gauze. The electric signal, which is the input to the CRT, are fed to this grid. The brightness of pattern, which is the output of the CRT, on the screen is controlled by varying the negative potential on the grid with respect to the cathode. The thermions come out of the hole in the anode in the form of a fine beam.
2. Deflecting system
The deflecting plates consist of two pairs of flat plates. One pair of plates is kept horizontal. These are called Y- plates. The other pair of plates is placed vertical. These are called X – plates. All the plates are kept with their planes parallel to the electron beam.
When a potential difference is applied across any pair of plates, an electric field is set up between the plates. Due to this electric field the electron beam gets deflected. The Y – plates deflect the beam in the vertical direction, while the X – plates deflect the beam in the horizontal direction
3. florocent screen
The fluorescent screen is a flat glass plate placed at the end of the tube. Its inside surface is coated with a fluorescent material.
The electron beam on striking the screen gives a bright spot thus converting the passing electrical signal into the visual pattern observed on screen. The bright spot is due to the coating of fluorescent material on the screen.
Image result for cathode ray tube diagram

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