Number of electrons when something is charged

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    Charged Electrons
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Discussion Overview

The discussion revolves around the question of how the number of excess electrons compares to the total number of atoms in charged objects. It explores various scenarios, including ultracapacitors, lightning, and everyday charging methods, focusing on both theoretical and practical implications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that the number of excess electrons when something is charged is generally small compared to the total number of atoms, particularly on Earth.
  • One participant provides an example of a 2600 farad, 2V ultracapacitor, noting it can store 5200 coulombs, which translates to approximately 3.2 * 10^22 elementary charge units, while the mass of the ultracapacitor corresponds to about 10^25 atoms.
  • Another example discusses lightning, indicating that an average bolt of negative lightning carries around 15 coulombs, equating to about 9.4 * 10^19 elementary charge units, compared to roughly 10^25 atoms in a cubic meter of air.
  • A participant mentions charging ordinary objects, such as balloons, which typically involve charges on the order of tens of nanocoulombs (about 10^11 electron charges), suggesting that the number of atoms in a typical balloon is many orders of magnitude larger.
  • One participant clarifies that "something is charged" can refer to both an excess and a shortage of electrons, indicating a broader interpretation of the concept of charging.

Areas of Agreement / Disagreement

Participants generally agree that the number of excess electrons is small compared to the total number of atoms in various examples discussed. However, there is a lack of consensus on the implications of charging due to both excess and shortage of electrons.

Contextual Notes

Some limitations include the dependence on specific conditions, such as the type of object being charged and environmental factors. The discussion does not resolve the complexities of how charging mechanisms may vary across different contexts.

jperentosh
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When something is charged, is the number of excess electrons a large or small number when compared to the total number of atoms?
 
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On Earth, usually very small.

Consider a 2600 farad, 2V ultracapacitor, which is one of our best devices for storing charge. We can store 5200 coulombs, which is about 3.2 * 10^22 elementary charge units. The ultracapacitor has a mass of about 0.5kg, which is probably somewhere along the lines of 10^25 atoms, roughly.

Consider lightning. Wikipedia says that an average bolt of negative lightning carries 15 coulombs, which is 9.4 * 10^19 elementary charge units. On the other hand, a cubic meter of air has on the order of 10^25 atoms.
 
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When you charge ordinary objects, e.g. by rubbing a balloon with fur, the amount of charge involved is on the order of tens of nanocoulombs (10-8 C), i.e. about 1011 electron charges. I leave it to you to estimate the number of atoms in a typical balloon, but it's surely many orders of magnitude larger.

We measure the charge in an introductory lab in which students charge up two balloons, then suspend them on strings hanging from the same point. The balloons repel to form an inverted V. By measuring the distance between the balloons and the length of the strings, and assuming the charges are equal, one can calculate the charge using a force diagram for one of the balloons.
 
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jperentosh said:
When something is charged, is the number of excess electrons a large or small number when compared to the total number of atoms?

Please note that when you say "something is charged", it need not always be due to excess of electrons. It can easily be due to shortage of electrons.

Zz.
 

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