Why losing charges under light?

In summary, the conversation discusses the process of xerography and how it involves the use of a special material that is conductive when exposed to light. The material is initially charged with static electricity and then exposed to light, causing the charged areas to lose their charge. This allows for the transfer of toner onto a sheet of paper, which is then permanently adhered through heating. The process is known as the photo-electric effect and typically results in a negative charge. The conversation also mentions the presence of ozone gas near copy machines, which is a result of the charge transfer process.
  • #1
oem7110
151
0
Does anyone have any suggestions on what charge of static electricity is being applied into the material?
When this material is exposed to light the areas exposed lose the charge, Does anyone know what kind of process it is for losing the charge under light?
Thanks in advance for any suggestions

"For xerographic copier, a special type of material is used, which is non-conducting in darkness but conductive when exposed to light. While in the dark the materials is charged with static electricity. When it is exposed to light the areas exposed lose the charge, while most not exposed retain the charge. After exposure to light the plate is sprayed with a fine powder of oppositely charged dry ink (toner), which adheres to the areas of the plate, which retained a charge by electrostatic attraction. Finally, a sheet of paper, which is also charged is placed on the plate, and the toner is transferred to the paper. The paper is then heated briefly to make the toner adhere permanently. The excess toner is scraped off the plate, and the entire plate is exposed to light to remove any remaining charge."
 
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  • #2
Does anyone know what kind of process it is for losing the charge under light?
Photo-electric effect.

The exact charge applied depends on the xerox machine.
 
  • #3
Simon Bridge said:
Photo-electric effect.

The exact charge applied depends on the xerox machine.

Usually, we can smell ozone gas near the copy machine,
Do you have any suggestions whether the materials is charged with negative or positive static electricity before photo-electric effect?
Thanks you very much for any suggestions
 
  • #4
oem7110 said:
Usually, we can smell ozone gas near the copy machine,
Do you have any suggestions whether the materials is charged with negative or positive static electricity before photo-electric effect?
Thanks you very much for any suggestions

It is negative charge. The ozone smell happens to be noticed at older machines. Newer ones have a charge roller which is in direct contact with the image drum. Lower voltage too. The laser or the LEDs is lit on the image drum. The charge changes and the negative charged toner will "jump" towards these lit areas.

Vidar
 
  • #5
Low-Q said:
It is negative charge. The ozone smell happens to be noticed at older machines. Newer ones have a charge roller which is in direct contact with the image drum. Lower voltage too. The laser or the LEDs is lit on the image drum. The charge changes and the negative charged toner will "jump" towards these lit areas.

Vidar

Thanks everyone very much for your suggestions
 

1. Why do charges get lost under light?

Charges can get lost under light due to a process called photoelectric effect, where light energy is absorbed by the charges and causes them to be emitted from the material. This can also happen due to other phenomena such as photovoltaic effect and photoconductive effect.

2. How does light cause charges to be lost?

Light carries energy in the form of photons, which can interact with the charged particles in a material and transfer their energy. This energy can either excite the charges to higher energy levels or completely free them from the material, resulting in loss of charges.

3. Can all types of light cause charges to be lost?

No, only certain types of light can cause charges to be lost. This depends on the energy of the photons in the light, which must be sufficient to excite or free the charges in the material. For example, ultraviolet and higher frequency visible light can cause charges to be lost, while lower frequency visible light may not have enough energy to do so.

4. Is loss of charges under light a reversible process?

Yes, loss of charges under light is a reversible process. The emitted charges can be captured and returned to the material through various techniques such as using an electric field or a material with a different work function. This allows for the study and utilization of the photoelectric effect in various fields.

5. Can the loss of charges under light have practical applications?

Yes, the loss of charges under light has many practical applications in fields such as solar energy, photodetectors, and photoemission spectroscopy. Understanding and controlling this phenomenon is crucial in developing these technologies and advancing scientific research.

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