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Air Cleaners and Xerox

Electric Charge

  • Fundamental Charge Units:
    • Electron: Negative charge.
    • Proton: Positive charge.
    • There are no smaller electric charges.
  • Benjamin Franklin's Observations:
    • Silk rubbed on glass results in a positive charge.
    • Fur rubbed on rubber results in a negative charge.
  • Measurement of Charge:
    • Charge is measured in Coulombs (C).
    • 1 Coulomb is equal to approximately \(6.28 \times 10^{18}\) charges.
  • Practical Example:
    • Dragging your feet on the carpet during winter can generate about \(-1 \times 10^{-6}\) Coulombs of charge.
  • Neutral Objects:
    • Neutral objects have both negative and positive charges in equal amounts.
  • Positively Charged Objects:
    • An object is positively charged when it has more positive charges than negative charges.
  • Negatively Charged Objects:
    • An object is negatively charged when it has more negative charges than positive charges.

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Electric Force

  • Like Charges Repel; Unlike Charges Attract:
    • Similar electrical charges repel each other.
    • Opposite charges attract each other.
  • Influence of Distance on Force:
    • The closer the charges, the stronger the force between them.
  • Coulomb's Law:
    • The formula is represented as \(F = \frac{k \cdot q_1 \cdot q_2}{R^2}\), where:
      • \(F\) is the force between the charges.
      • \(k\) is Coulomb's constant.
      • \(q_1\) and \(q_2\) are the amounts of the charges.
      • \(R\) is the distance between the charges squared.
  • Proportionality of Force:
    • The force is proportional to the product of the charges divided by the distance between them squared.

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Voltage

  • Power Supply Function:
    • The power supply (battery) pushes current around the circuit.
  • Battery Polarity:
    • The battery maintains one side as positive and the other as negative.
  • Energy Conversion:
    • Work is done in lighting the bulb, and this work comes from the charges in the circuit.
  • Source of Energy:
    • The energy for this work comes from the battery.
  • Voltage Defined:
    • Voltage measures the potential energy of a unit of charge at a particular location.

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  • Potential Energy in Positive Charge:
    • Positive charge has some potential energy as it wants to move to the negative terminal.
    • As it moves to the negative terminal, it releases energy in the bulb, lighting it up.
  • Efficiency and Light Output:
    • A positive charge with much more potential energy releases more energy into the light bulb.
    • This results in the light bulb glowing brighter.

Dust

What is Dust?

  • Composition:
    • Dust: Consists of tiny pieces of rock, dirt, and organic matter.
    • Soot: Carbon and organic material that has been burned imperfectly; characteristics include being oily, greasy, and tar-like.
    • Ash: Powdery non-combustible residue left after a fire.
  • Behavior:
    • Dust particles are basically neutral particles floating in the air.

Dust Filters

  • Filtering Dust:
    • Dust can be filtered by passing air through small pores; air goes through, but large dust particles get trapped.
  • Dust Dynamics:
    • Dust floats around due to various forces:
      • Gravity: Pulls dust particles down.
      • Buoyancy: Keeps dust particles up.
      • Air Resistance: Slows the movement of dust particles.
      • Air Currents: Move dust particles around.

Electronic Air Cleaner

  • Operation:
    • Air is blown through an electronic air cleaner.
  • Charging Mechanism:
    • Negatively charged dust particles stick to positively charged walls within the cleaner.

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Electrostatic Precipitator Operation

  • Power Supply:
    • A power supply is used between walls and corona wires.
  • Corona Discharge:
    • Corona discharge from negatively charged wires releases electrons into the air.
  • Charging Dust Particles:
    • These electrons charge the dust particles, making them negatively charged.
  • Dust Collection:
    • The negatively charged dust is then attracted to the positively charged walls, trapping the dust.
  • Force Comparison:
    • The electrostatic force that captures the dust is much stronger than gravity and air currents, effectively immobilizing the dust particles against the walls.

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Ion Generator in Air Cleaning

  • Ion Generation:
    • The ion generator charges dust particles but does not trap them.
  • Particle Behavior:
    • Instead, the charged dust sticks to the neutral walls of the room or the furniture.
  • Polarization Effect:
    • The charged dust particle polarizes the neutral surface, causing them to attract each other.

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Xerox Machines

  • Copying Process:
    • An image is copied onto paper using toner particles, which are colored plastic particles.
  • Toner Application:
    • The goal is to place toner on the paper exactly where there is writing on the original.
  • Underlying Principle:
    • Electrostatics: The process relies on electrostatic principles to transfer the toner to the paper.

Photoconductor Behavior

  • In darkness:
    • Acts as an Insulator - does not conduct electricity.
  • In light:
    • Becomes a Conductor - conducts electricity.
    • The level of conductivity increases with more light exposure, decreasing the resistance to charge flow.

Photoconductors change their conductivity based on the amount of light they are exposed to, making them useful in various applications such as in photocopiers and light-sensitive devices.

Charged Photoconductor

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Xerox Machine

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Image Transfer

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Laser Printer

Use laser to scan an image onto a photoconductive drum This creates a charge image on the drum that can be covered with toner This toner is then transferred to the paper, creating the image