Voltage & Capacitors: How Does It Create Charge?

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Discussion Overview

The discussion revolves around the relationship between voltage and charge in capacitors, particularly how voltage influences charge accumulation when a capacitor is connected to a battery. Participants explore theoretical aspects, definitions, and equations related to electric energy storage in capacitors.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant asserts that the charge (Q) on a capacitor is proportional to the potential difference (V) across its plates, suggesting that voltage causes charge accumulation.
  • Another participant counters that charge is a fundamental quantity and that voltage is defined as work per unit charge, implying that voltage does not "cause" charge but rather describes the energy associated with moving charge.
  • A participant raises a point of confusion regarding the relationship between voltage, work, and energy storage in capacitors, referencing the equation for electric energy storage (U = 1/2 QV).
  • Another participant agrees that potential difference is related to charge but clarifies that charge is not created; rather, electrons flow into the capacitor due to chemical reactions in the battery until the capacitor's voltage matches that of the battery.
  • Further elaboration includes the relationship between capacitance (C), charge (Q), and voltage (V), with equations provided to illustrate these connections.

Areas of Agreement / Disagreement

Participants express differing views on whether voltage causes charge accumulation, with some asserting a causal relationship while others emphasize the fundamental nature of charge itself. The discussion remains unresolved regarding the interpretation of these concepts.

Contextual Notes

Participants reference various equations and definitions, indicating potential limitations in understanding the relationships between voltage, charge, and energy storage. There is an ongoing exploration of how these concepts interrelate without reaching a consensus.

Who May Find This Useful

This discussion may be of interest to students and enthusiasts of physics and electrical engineering, particularly those seeking to understand the principles of capacitors and the interplay between voltage and charge.

gkangelexa
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For a given capacitor that is connected to a battery, the amount of charge acquired by each plate is proportional to the magnitude of the potential difference V between them.
Q = CV

Is it correct to say that the voltage (potential difference V) applied across the capacitor plates is what causes the charge?
How does the voltage from the battery create the charge?


thanks!
 
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No. Charge is a fundamental quantity, along with time, mass, & length. Voltage is a ratio of work to charge. Voltage from a to b is defined as the work per unit charge expended transporting a charge from a to b.

Charge is basic. Voltage is defined in terms of work & charge. Nothing "causes charge" that we know of. Charge just basically is & that's all we can say.

Claude
 
Claude,
You reminded me of another point of confusion...
voltage is work/ charge... V = -W/q = (U2-U1)/q... since the difference in potential energy is equal to the negative of the work done.

How do you relate those equations to this one concerning Electric energy storage in a capacitor? U = 1/2 QV
 
yes, we can say Potential differencce is cause for the charge but it does not mean that charge is created.

when a battery is connected to a circuit , the electrons are produced due to the chemical reactions in the battery .These electrons flow into the capacitor and the voltage
across the capacitor rises until the supply voltage and the electrons flow stops .

once the capacitor is charged the voltage of the capacitor is same as that of the battery.
 
gkangelexa said:
Claude,
You reminded me of another point of confusion...
voltage is work/ charge... V = -W/q = (U2-U1)/q... since the difference in potential energy is equal to the negative of the work done.

How do you relate those equations to this one concerning Electric energy storage in a capacitor? U = 1/2 QV

By definition C = Q/V, i.e. 1 farad = 1 coulomb / volt. Then Q = CV. U = (1/2)QV = (1/2)(CV)V = (1/2) C V^2.

Claude
 

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