How Everything Works
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QUESTIONS AND ANSWERS
 
Xerographic Copiers
Page 2 of 3 (22 Questions and Answers)

1347. Can the electric current be taken out of the metal where the charge will not carry?
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While charges can move freely through a metal, allowing the metal to carry electric current, it's much harder for charges to travel outside of a conductor. Charges can move through the air or through plastic or glass, but not very easily. It takes energy to pull the charges out of a metal and allow them to move through a non-metal. Most of the time, this energy requirement prevents charges from moving through insulators such as plastic, glass, air, and even empty space.

1348. Does an MRI work in the same way as a copier (or puts you in a magnetic field and copies an image of your body)?
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No, an MRI uses a very different technique for imaging your body. A copier uses light to examine the original document while an MRI machine uses the magnetic responses of hydrogen atoms to map your body.

1349. How do dryer sheets diminish the clothes' static?
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They leave a layer of conditioning soap on the clothes and this soap attracts moisture. The moisture conducts electricity just enough to allow static charge to dissipate.

1350. How do you get static out of hair?
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If you put a conditioner on your hair, it will attract enough moisture to allow static charge to dissipate.

1351. How does one create an electric or magnetic field?
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The simplest way to make these fields is with electric charges (for an electric field) or with magnets (for a magnetic field). Charges are naturally surrounded by electric fields and magnets are naturally surrounded by magnetic fields. But fields themselves can create other fields by changing with time. That's how the fields in a light wave work—the electric field in the light wave changes with time and creates the magnetic field and the magnetic field changes with time and creates the electric field. This team of fields can travel through space without any charge or magnets nearby.

1352. If electrons can't change levels, how can a photoconductor help them change one level to another?
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In a metal, electrons can easily shift from one level to another empty level because the levels are close together in energy. In a full insulator, it's very difficult for the electrons to shift from one level to an empty level because all of the empty levels are far above the filled levels in energy. In a photoconductor, the empty levels are modestly above the filled levels in energy, so a modest amount of energy is all that's needed to shift an electron. This energy can be supplied by a particle or "photon" of light. An illuminated photoconductor conducts electricity.

1354. Are black lights less or more conducive to charging the particles in film?
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They are generally more conducive. Black light is actually ultraviolet light and its photons carry more energy than any visible photon. They can cause chemical changes in many materials, including skin.

1355. Does this photoconductor stuff have to do with why you can only develop film in the dark?
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Yes. Particles of light, photons, cause chemical changes in the film. You can work with some black-and-white films in red light because red light photons don't have enough energy to cause changes in those films. However, color film and most modern black-and-white films require complete darkness during processing. If you expose them to any visible light, you'll cause chemistry to occur.

1356. How do color copiers work?
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They assemble 4 colors, yellow, cyan, magenta, and black together to form the final image. The photoconductor creates charge images using blue, red, green, and white illumination successively and uses those images to form patterns of yellow, cyan, magenta, and black toner particles. These particles are then superimposed to form the final image, which appears full color. Naturally, the photoconductor used in such a complicated machine must be sensitive to the whole visible spectrum of light.

As one of my readers (Tom O.) points out, most modern color copiers are essentially scanners plus color printers. They use infrared lasers to write the images optically onto four light-sensitive drums, one drum for each of the four colors (some systems reuse the same drum four times).


1357. Is the red light effect in xerographic copiers the same concept behind red lights in a darkroom? Does film have the same sort of properties?
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Yes. The light sensitive particles in black-and-white photographic paper don't respond to red light because the energy in a photon of red light doesn't have enough energy to cause the required chemical change. In effect, electrons are being asked to shift between levels when the light hits them and red light can't make that happen in the photographic paper. However, most modern black-and-white films are sensitive to red light because that makes roses and other red objects appear less dark and more realistic in the photographs.

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