The focused and accelerated electron beam can thus be

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: oltage applied to the control grid, larger will be the number of electrons that will be allowed to strike the screen, and larger will be the beam's intensity. If the grid voltage is negative, then no electrons will be allowed to pass the grid and the beam is said to be blanked. The electrons, which are allowed to pass through the control grid are accelerated and focused by an assembly unit consisting of accelerating electrodes and a focusing electron lens. The accelerating electrodes are applied with a positive voltage to accelerate the electrons and the focusing electron lens consists of a cylindrical metal enclosure with a hole through which the electrons pass in the form of an electron beam. The electron beam generator, the control grid, and the accelerating electrodes with focusing electron lens together form the electron gun of the CRT monitor. To focus the electron beam generated by the electron gun at a desired point on the screen, the beam is passed through a pair of vertical deflection plates and a pair of horizontal deflection plates. Appropriate positive voltages are applied to one of the vertical and one of the horizontal plates to achieve this. For example, the beam can be moved up/down by applying a suitable positive voltage to the top/bottom plate of the vertical plates pair. Similarly, the beam can be moved left/right by applying a suitable positive voltage to the left/right plate of the horizontal plates pair. The focused and accelerated electron beam can thus be made to hit at any point on the screen. The backside of the monitor's screen is coated with phosphor, a chemical that glows for a short time when it is hit by the electron beam. The screen's phosphor coating is organized into a grid of dots called pixels (a contraction of picture elements). Since the phosphor glows only for a short time (few microseconds), an image drawn on the screen would be visible only for a few microseconds and then fade away, unless the image is repeatedly drawn. This may appear to be an inconvenience, but it is also an advantage since there is no need to erase anything. Instead, we just need to draw new images a...
View Full Document

Ask a homework question - tutors are online