Experiment: my like charges didn't repel

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Discussion Overview

The discussion revolves around an experiment involving charged aluminum foil and the expected electrostatic repulsion between like charges. Participants explore the setup, configuration, and physical properties affecting the observed behavior of the foils under a high voltage DC source.

Discussion Character

  • Experimental/applied
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes a setup with a 5kV DC device connected to aluminum foil, expecting a repulsive effect between the foils but observing no movement.
  • Another participant requests clarification on the configuration of the foils and the ground plane to better understand the electric field shaping.
  • A participant notes that in a previous setup, the foils were attracted to each other, suggesting that charge accumulation should lead to repulsion.
  • Questions are raised about the mass of the foil and its potential impact on the observed electrostatic forces.
  • One participant suggests that the mass of the foil might be too great for noticeable repulsion to occur.
  • Another participant estimates the capacitance between the foils and the ground plane, indicating that the resulting charge may be insufficient to overcome gravitational forces and cause deflection.

Areas of Agreement / Disagreement

Participants express differing views on the reasons for the lack of repulsion, with some attributing it to the mass of the foil and others to the configuration and charge accumulation. No consensus is reached regarding the primary cause of the observed behavior.

Contextual Notes

Participants mention factors such as the weight of the foil, the configuration of the setup, and the capacitance involved, but these aspects remain unresolved and depend on specific assumptions about the experimental conditions.

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i had a battery powered device that outputted 5kV DC . i hooked up one of the output leads to two long pieces of Al foil. i was expecting a repulsion but nothing happened, why? is the voltage not high enough?
 
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A few more details might help --- are you arranging the foil as the leaves in a leaf electrometer? Or, just hanging off a terminal of the power supply? What's the configuration of your "ground plane?" (What's connected to the other terminal to "shape" the electric field?)
 
previous setup
QyOOXNe.png

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i hooked up each foil to the opposite ends of the device and the foils were attracted to each other, which is good news but i was going for a repulsive effect. charge should be accumulating at the ends of both terminals of the device so i figured either end should have half the amount of ΔV.
anyway, in the first setup (image), i didn't notice the foils moving at all and i don't know why.
 
How heavy is the foil?
 
judging from your reply i take it the foils should have repelled, they were probably just too massive?
 
That would be my guess --- hit Wiki, or Google around a bit for capacitance formulae, and you'll find the capacitance between your leaves and the ground plane is going to be in the neighborhood of hundredths of picofarads, times the 5kV is a charge of a few picocoulombs on the leaves; split that charge, tuck it into coulomb repulsion, and it's not going to be enough to noticeably deflect the leaves from each other in the Earth's gravitational field. The foil wrap that used to be on Nestles bars was around 0.0005" and just barely moved for carpet static on a nice dry winter day.
 

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