Category: television

If you stand between the two satellites, would you have light on you?

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If you stand between the two satellites, would you have light on you?

When two satellites beam their radio waves at you, you are exposed to both of those waves. A normal antenna would not be able to distinguish between them and it would be hard to receive the transmissions of one and not the other. But with a satellite dish, you can easily select the transmissions of one and exclude those of the other. The satellite dish is directional, meaning that it focuses and collects radio waves from a particular direction while ignoring those from other directions. With a satellite dish aimed at a particular satellite, you can receive only transmissions from that satellite.

What is one doing when changing the brightness, contrast, and color adjustments …

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What is one doing when changing the brightness, contrast, and color adjustments on a television?

The brightness control determines the maximum strength of the electron beam and thus the peak brightness of the phosphors on the screen. The contrast control determines the extent to which the electron beam current changes between bright regions and dim regions on the screen. If the contrast is high, then even a less-than-white spot in the image may produce full beam current and full brightness in the phosphors and a more-than-black spot in the image may be cast as full black (no beam at all). If the contrast is low, then almost the entire screen will be illuminated by a medium electron beam and the image have no full black or full white. The color adjustments control the relative intensities of the red, green, and blue guns. Because of the way color is encoded in the television signal, the traditional controls are hue and tint, which involve mixtures of red, green, and blue. All these controls involve adjustments to the voltages and currents in the electron guns (cathodes), grids, and anodes of the picture tube.

How can computer monitors and televisions have images burnt into them over time?

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How can computer monitors and televisions have images burnt into them over time?

As the electron beam collides with the phosphor coating on the inside of the picture tube, it slowly damages that phosphor coating. Eventually the phosphors are burnt away and the inside surface of the picture tube stops being uniform. To avoid burning specific regions more than others, computers use screen savers that darken the images by turning down the electron beam and keep those images moving about randomly.

How can the magnets be manipulated in such a way that they can do this moving of…

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How can the magnets be manipulated in such a way that they can do this moving of the electron beam in such an incredibly small amount of time?

The electromagnets that control the beam are able to turn on and off very quickly. The only limit on the rate at which they can change the magnetic field comes from their inductance. They do resist changes in current passing through them. Fortunately, the television doesn’t move the beam about randomly; it sweeps the beam smoothly. Thus the changes in the current through the electromagnetic coils are also smooth. The television has no trouble ramping the field through the horizontal sweep coils back and forth every 1/15,750th of a second.