Van de graaff generator as a current source

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Discussion Overview

The discussion revolves around the feasibility of using a van de Graaff generator as a current source, particularly in the context of measuring the time required to reach maximum voltage. Participants explore the theoretical implications and practical challenges of this approach, touching on concepts of current, voltage, and efficiency.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that grounding the positive terminal of the generator while connecting a resistor to the negative terminal could create a current, suggesting a method to derive current using simple formulas.
  • Others argue that while the method may be theoretically feasible, it would result in a very low current output compared to the energy input, indicating a significant inefficiency.
  • One participant mentions calculating the efficiency and finding it to be extremely low.
  • Several participants express uncertainty about the practicality of measuring the time to reach maximum voltage using this method, with questions raised about the grounding of wires and the resulting voltage on the sphere.
  • A participant suggests that by grounding the generator and measuring the current, they could determine the time to maximum voltage, proposing a formula based on the assumption of constant current.
  • Another participant challenges the idea by stating that grounding the wires or running the output through a resistor would not yield any voltage on the sphere, indicating a misunderstanding of the proposed method.
  • One participant clarifies that grounding the sphere allows the generator to act as a current source, suggesting a method to measure current through a high resistance to determine voltage.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the feasibility of using the van de Graaff generator as a current source. There are competing views regarding the practicality and efficiency of the proposed method, with some expressing skepticism about the underlying assumptions.

Contextual Notes

Limitations include uncertainty about whether the current is constant, the dependence on specific configurations of grounding and resistance, and unresolved mathematical steps in deriving the proposed formulas.

abdo799
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I know that van de graaff generator is a high voltage generator, i was wondering though if we can use it as a current source, if we get any resistor, connect the negative terminal to the generator "if the generator generates negative charge " then ground the positive terminal, then any charge that appears on the sphere will be immediately pulled to ground, creating a current, using simple formulae we can derive the current, is that feasible or not?
 
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abdo799 said:
I know that van de graaff generator is a high voltage generator, i was wondering though if we can use it as a current source, if we get any resistor, connect the negative terminal to the generator "if the generator generates negative charge " then ground the positive terminal, then any charge that appears on the sphere will be immediately pulled to ground, creating a current, using simple formulae we can derive the current, is that feasible or not?
Sure, it's feasible as far as I can see but it is a HUGE waste of electricity to do that since the amount of current you'll get is tiny vs the amount you have to use to get it.
 
Yea i know, i calculated it, and the efficiency was extremely low
 
Just wanted to know if it would work, going to use it to measure how much time does my generator need to reach maximum voltage
 
abdo799 said:
Just wanted to know if it would work, going to use it to measure how much time does my generator need to reach maximum voltage
I don't get how you could do that.
 
My plan is by grounding the generator and measuring the current in the wires i can use it to know the time to reach the maximum voltage, can't write the formula now because i am using the mobile app
 
abdo799 said:
My plan is by grounding the generator and measuring the current in the wires i can use it to know the time to reach the maximum voltage, can't write the formula now because i am using the mobile app
Assuming I=const the formula is simply t=Vmax⋅C/I
 
I don't know yet if I is constant, but theoretically, it should be
 
abdo799 said:
My plan is by grounding the generator and measuring the current in the wires i can use it to know the time to reach the maximum voltage, can't write the formula now because i am using the mobile app
I still don't get it. If you ground the wires, or run the output of the generator through a resistor, you won't GET any voltage on the sphere. I think you must be talking about something that I'm not following.
 
  • #10
That's the whole idea, i don't need any voltage, by grounding the sphere, the generator became a current source, so i measure the current in the wire, or my case i will connect a high resistance and measure the voltage across it because the current will be low and hard to measure.
The maximum voltage of a van de graaff generator is 3*10^6*radius(in meter), and the voltage on the sphere is kQ/r where K is coulomb's constant
Q=I*t and we're done
 

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