How computer emits Radiation?

          

  Since computers are electrically powered they must emit radiation of some sort-but how is it different to the negligible and harmless levels of radiation emitted by other domestic and business electrical appliances? As far as the system unit is concerned, it is not. The only source of emissions within the system unit is the power supply, which conforms to the same specification as any other electrically powered apparatus. The real threat comes from the monitor, which contains the control mechanisms for displaying screen images. An electron gun, which receives instructions from the graphics adapter card fires electrons at the phosphor, coated screen, causing the phosphor to glow. This process is harmless; it is the mechanism controlling the movement of the electron gun, which represents a potential health hazard. The beam of electrons is accelerated and directed towards the screen by a high voltage transformer, but it requires extra navigational power to move arrow and down the screen during raster scanning. This is achieved by a horizontal and vertical deflection system: two sets of coils are wound around the neck of the cathode ray tube and, when the monitor is switched on, electric currents flow through these coils (or yokes) and generate powerful magnetic fields. The magnetic power of these coils is able to deflect the electrons as they are fired from the gun-a horizontal deflection coil moves the beam from left to right; a vertical deflection coil moves it from top to bottom. Each time the electron beam reaches the right-hand side of the screen, a synchronization pulse causes it to ‘fly-back’ to the left-hand side while the vertical deflection coil pulls it down a line. Typically, monitors produce  line pictures a second and the electron beam travels back and forth across the screen more than 15000 times a second. This amounts to a horizontal scan frequency-or line refresh rate-of 15000 hertz (15 kilohertz); and a vertical scan frequency –or frame refresh rat (the entire pictures)-of 60 hertz.

            This process of image creation in the cathode ray tube gives rise to three types of monitor emissions:

·                     X-rays, caused by the impact of the electron beam on the inside of the glass

·                     Harmless electrostatic potential caused by positive voltage on the glass.

·                     Alternating electromagnetic fields caused by the power supply and deflection yokes.

The powerful filed of electromagnetism generated by the deflection yokes is the source of radiation thought to be harmful to living cells. The pulsing action of the fly-back mechanism generates a corresponding electromagnetic pulse of VLF radiation; whilst the slower vertical deflection coil produces a strong pulse of much lower 60 hertz ELF radiation.

            The monitor is designed to minimize the extent to which such radiation can hurt a lead lining inside the screen eliminates X-rays almost completely and the glass and casing of the monitor absorb the vast majority of the remaining VLF radiation. Some, however, leaks out mostly from the back, where the coils are located, some at the side and a little at the front. What this means, in physical terms, is that the cyclical movement of the electromagnetic field continues to act beyond the confines of the monitor. An electromagnetic field is composed of charged particles oscillating (using energy to move back and forth) at a frequency measured in hertz.

            The frequency at which particles in a particular field oscillate (60 hertz for ElF and 15 kilohertz for VLF radiation) is called the resonant frequency, where resonance describes the frequency at which particles will oscillate most freely. All particles (whether in solid, liquid or gaseous form) have a resonant frequency- what the frequency is depends on the chemical composition of that particle. When a field encounters panicles, which share its resonant movement of a poorly designed suspension bridge: if air currents have been channeled into a particular frequency (by the location of nearby hills, for example) and hit a suspension bride, the bridge may begin to move in the same way as the air current. If the two prove to have the same resonant frequency, the bridge will assume the patterns of oscillation of the air and use its energy to move. The ‘ripples’ of the bridge will continue to increase in size until the whole structure collapses.