What is the principle of the Trinitron Sony TV system?

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What is the principle of the Trinitron Sony TV system? — JPD, Spiennes, Belgium

To form a color image, a color television illuminates a dense pattern of tiny spots—some red, some green, and some blue. By mixing various amounts of these three primary colors of light, the color television can make us perceive any color. But the television must control the amounts of these three colors at each spot on the screen, a very difficult task. A typical color television does this by shining three separate beams of electrons through a mask with holes in it and onto a screen that’s covered with tiny phosphor spots. Because the three beams approach the mask at different angles, they illuminate different portions of the screen after passing through the holes. Thus the “blue” beam only illuminates spots of blue phosphor, the “red” beam illuminates red spots, and the “green” beam illuminates green spots.

However, the Sony Trinitron system uses a line mask rather than one containing holes and the phosphors are coated onto the screen in stripes rather than spots. Again, three separate electron beams are used but they now illuminate specific stripes of phosphor rather than spots of phosphor. The advantage of the stripe approach is that there is more active phosphor on the screen (fewer dark places between spots) so the image is brighter.

Is it possible to sense when a person touches a car, even if the car is painted?…

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Is it possible to sense when a person touches a car, even if the car is painted? – AW

Yes. I wouldn’t try to detect mechanical contact, because you’d have trouble differentiating between forces exerted on the car by a hand and those exerted on it by sound waves. But you can tell whether a conducting object (such as a person) is near the car by looking at the car’s electric properties. If you were to send electric charge on and off the car rapidly with a source of high-frequency alternating current, you would find that the amount of charge that flowed on or off the car during each cycle would change as the person’s hand approached the car. That’s because the charges on the car would push or pull on charges in the person’s hand and the charges in the person’s hand would move. In effect, the person’s hand would make the car “larger” and it would draw more charge from your current source. Even if the person didn’t touch the car, the nearness of the hand and car would change the way current flowed on and off the car. Such a change would be easy to detect with laboratory equipment and could probably be made by cheap consumer equipment, too. The only complications would be in not detecting everything—passing cars for example—and in not damaging the device with static discharges. Still, I think all of that could be done.

How does an electric motor work? – BR

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How does an electric motor work? – BR

An electric motor uses the attractive and repulsive forces between magnetic poles to twist a rotating object (the rotor) around in a circle. Both the rotor and the stationary structure (the stator) are magnetic and their magnetic poles are initially arranged so that the rotor must turn in a particular direction in order to bring its north poles closer to the stator’s south poles and vice versa. The rotor thus experiences a twist (what physicists call a torque) and it undergoes an angular acceleration—it begins to rotate. But the magnets of the rotor and stator aren’t all permanent magnets. At least some of the magnets are electromagnets. In a typical motor, these electromagnets are designed so that their poles change just as the rotor’s north poles have reached the stator’s south poles. After the poles change, the rotor finds itself having to continue turning in order to bring its north poles closer to the stator’s south poles and it continues to experience a twist in the same direction. The rotor continues to spin in this fashion, always trying to bring its north poles close to the south poles of the stator and its south poles close to the north poles of the stator, but always frustrated by a reversal of the poles just as that goal is in sight.

How far can electricity be transferred over wires from a power station before th…

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How far can electricity be transferred over wires from a power station before the loss factor is too great? — JD, New York NY

That depends on the electricity’s voltage. The transmission lines carrying the electricity are important parts of the overall electric circuit. They waste electric power as they carry current and the amount of power they waste is proportional to the square of the current they carry. The purpose of high voltage transmission lines is to send as small a current as possible across the countryside so that the wires waste as little power as possible. This reduction in current is possible if each electric charge moving in that current carries a large amount of energy—the current must be one that consists of high voltage charges. In short, higher voltage transmission lines employ smaller currents and waste less power than lower voltage transmission lines.

When Thomas Edison set out to electrify New York City, he used direct current of the highest practical household voltage. Nonetheless, his relatively low voltage power transmission lines wasted so much power that he had to scatter generating plants throughout the city so that no home was far from a power plant. But when George Westinghouse and Nicola Tesla realized that using alternating current and transformers to temporarily convert the household power to high voltages and small currents, they were able to send power long distances without wasting electricity. That realization eventually destroyed Edison’s direct current electric system and gave us the modern alternating current system. It’s now common to send electric power several hundred miles through high voltage transmission lines. At those distances, perhaps half the power is lost en route. I doubt that transmission of power more than 1,000 miles is practical.

How does an electric lighter work? – AW

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How does an electric lighter work? – AW

In a piezoelectric lighter, a spring-driven mass strikes a piezoelectric crystal and exposes that crystal to a sudden enormous strain. This strain changes the shapes of the electronic levels in the crystal and produces an imbalance in the electric charges on the crystal’s surfaces. One side of the crystal acquires a large positive charge, the other a large negative charge. The potential energies of these imbalanced charges are large enough that they have enormous voltages—typically 10,000 to 50,000 volts. With that much voltage (energy per charge), the charges can leap through the air for about a centimeter or more. If you allow these charges to pass through your hand, they will give you a mild shock—there aren’t enough charges moving to give you a dangerous shock.

What source of energy keeps the earth and the planets orbiting the sun or keeps …

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What source of energy keeps the earth and the planets orbiting the sun or keeps electrons orbiting the nuclei of atoms? – AW

It takes no additional energy to keep those objects orbiting—the earth’s inertia keeps it moving around the sun. If the sun weren’t there, the earth would continue forward in a straight line at a steady pace forever because that is how free objects behave. It takes no energy or force to keep them moving. But the earth is drawn continuously inward by the sun’s gravity and so it travels in an elliptical arc instead of a straight line. Assuming that nothing adds or subtracts energy from the earth and sun, the earth will continue to orbit the sun forever. The same applies for the other planets and for electrons orbiting nuclei in an atom. In the latter case, it is electromagnetic forces that draw the electrons inward, rather than gravity.

If you have a glass of water that is real cold but not frozen, can the addition …

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If you have a glass of water that is real cold but not frozen, can the addition of one normal ice cube make it all freeze? Can I do this in the kitchen? – D

The answer to both questions is yes. If you begin with very pure, dust-free water in a very clean glass, you should be able to supercool it below its normal freezing temperature of 32° F (0° C). That’s because water has difficulty forming the initial seed crystals upon which ice can grow. If you then add an ice crystal to the supercooled water, it should begin to freeze rapidly. While I have never done this myself, it shouldn’t be too hard. You should probably use distillated and filtered water and a brand new glass that you’ve cleaned thoroughly. Cover the water to keep out dust. Cool it carefully through 32° F in the freezer and then add a tiny ice chip. The water should begin to crystallize around that ice chip. A simpler example of this sudden freezing phenomenon is a heat pack—one containing sodium acetate. At room temperature, it contains a supercooled solution of sodium acetate that is unable to freeze spontaneously. When you press a button in the pack, you trigger the crystal formation and the whole pack freezes in seconds. The crystallization process releases enough thermal energy to keep the pack hot for hours. Incidentally, ski resorts regularly seed the water they use to make artificial snow with molecules that initiate crystal growth to avoid forming supercooled liquid. Doing so greatly enhances the amount of snow they make.

How does a silencer work?

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How does a silencer work? — AWG, Karachi, Pakistan

When a bullet emerges from the barrel of a gun, the high-pressure gas that is propelling it from behind abruptly enters the atmosphere. This sudden burst of pressurized gas is like that released by an exploding firecracker and produces a loud “pop” sound. A silencer slows down this gas’s entry into the atmosphere. Before leaving the gun, the bullet passes through a series of air-filled chambers. The gas behind the bullet must enter each chamber, one at a time, and with each passage, its pressure and energy decrease. By the time the gas emerges from the last chamber, its pressure is low enough that it makes only a weak “whoosh” sound as it enters the atmosphere. This same technique is used by an automobile muffler. However, a silencer is only effective with low-velocity bullets. If the bullet itself travels faster than the speed of sound (331 m/s), it will create shock waves as soon as it enters the atmosphere and will generate its own explosion noise—miniature “sonic booms.”

Is there a touch sensor that can sense when you touch the body of a car? – AW

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Is there a touch sensor that can sense when you touch the body of a car? – AW

The same touch sensors that are used in “touch” lamps or some elevator buttons could be used to sense when you touch a car. A car is essentially insulated from the ground by its rubber wheels, so that when you touch it there is a tendency for electric charge to be transferred between the earth and the car through you. That’s why you may receive a shock when you touch a car on a cold winter day. Many electronic devices are capable of detecting this charge transfer (in fact, many of them would be damaged by such sudden and large charge transfers). So building a car touch sensor would be easy. Whether there is a commercial product that does this is another matter, and I am not sure of the answer.

Do sparks generated by Tesla coils shock humans? If not, why not? – AW

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Do sparks generated by Tesla coils shock humans? If not, why not? – AW

A Tesla coil is radio-frequency transformer that produces small currents of very high-energy electric charges. A radio frequency alternating current passes through the primary coil of this transformer and it induces a current in the secondary coil of the transformer. The frequency of the alternating current must be extremely high because there is no iron in the core of the transformer to store energy during a cycle, so that each cycle must be very brief. Because the alternating current flowing out of the secondary coil of the transformer has a very high frequency, it travels over the surface of a conductor, rather than through its center. Thus when you allow that current to pass through you, it goes along your skin and not through your body. As a result, you barely feel its passage except perhaps as surface heating (however, it can cause what is called an “RF burn” in some cases.) Also, the current from a typical Tesla coil is very small so it would barely be noticeable even if it went through your body.