Charging an Insulator: Explained

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    Charged Insulator
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Discussion Overview

The discussion revolves around the mechanisms by which insulators can become charged, particularly through processes such as rubbing with another material and exposure to radiation or light. Participants explore both the triboelectric effect and the photoelectric effect in the context of insulators.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions how an insulator can become charged, noting the lack of free electrons in insulators.
  • Another participant explains that rubbing an insulator with another material can strip electrons from the surface, leading to a charge imbalance due to the triboelectric effect.
  • A participant expresses surprise at the role of surface chemistry in charging insulators, indicating a gap in their prior education on the topic.
  • It is mentioned that radioactive beta decay sources can charge insulators by embedding beta particles, and that photoelectric interactions from UV light or X-rays can eject electrons from insulators.
  • One participant raises a question about the applicability of the photoelectric effect to insulators, suggesting that it is typically associated with metals.
  • Another participant clarifies that while insulators have a higher work function, they can still undergo the photoelectric effect under certain conditions, such as with high-energy photons.

Areas of Agreement / Disagreement

Participants express varying levels of understanding about the charging of insulators, with some agreeing on the mechanisms like the triboelectric effect, while others debate the applicability of the photoelectric effect to insulators. The discussion remains unresolved regarding the specifics of these processes and their implications.

Contextual Notes

There are limitations in the participants' understanding of the underlying physics, particularly regarding the conditions necessary for the photoelectric effect in insulators and the role of surface chemistry in charging mechanisms.

ArielGenesis
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I feel so ashamed to ask a question this simple, but how does an insulator get charged? Let's say rubbing a glass rod with cat's fur. I thought that insulator means there is no free electron.

Does rubbing means turning the neutral atoms at the surface of the glass rod into ions?

or something else is happening?
 
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Yep, electrons are pretty much stripped off the surface of the insulator and transferred to the other object. Touching the two together forms a chemical bond, and if the surface chemistry is just right (e.g., one material has a higher surface electronegativity than the other one), then pulling them apart will result in an imbalance, leaving the surfaces charged with opposite polarities. When you rub the two together, you are essentially repeating this process many times over. It's called the triboelectric effect.
 
aha ic, so its surface chemistry, there were chemical reaction

these things were never taught in high or first year physics, no wonder i don't understand at all.

thanks
 
Also, if you have a strong radioactive beta-decay source near an insulator, betas can inbed themselves in the insulator and charge it up. In addition, visible or UV light or X-rays, through photoelectric interactions, can eject photoelectrons from the surface. In all these cases, because there is no conduction band in the insulator, the charges cannot be neutralized.
 
I thought photoelectric effect only happens in metals?
 
ArielGenesis said:
I thought photoelectric effect only happens in metals?
Insulators have a higher work function than metals, meaning it takes a higher energy photon to knock off an electron, but even insulators have electrons. The photons probably have to be vacuum-ultra violet (100 nm or shorter wavelength).
[Added edit] We also know that in the x-ray region, deep core photoejection (a form of photoelectric effect) can knock k-shell electrons out, which may escape the insulator. Outer electrons will then fill the k-shell, and leave a hole in the valence band. But since there are no electrons in the conduction band, the hole is not filled.
 
Last edited:
oooh ic thanks every1
 

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