Constant current for series resistance

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Discussion Overview

The discussion centers on the behavior of current in a series circuit with resistors of different resistances. Participants explore how constant current is maintained throughout the circuit and the implications of resistance on current flow and drift velocity.

Discussion Character

  • Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions how current can remain constant in a series circuit with resistors of different values, suggesting that current should decrease within each resistor.
  • Another participant explains that the total current in a series circuit is conserved and flows equally through each resistor, with voltage drops varying across the resistors.
  • A participant asks about the relationship between drift velocity, electron density, and how a single resistor affects the overall current in the circuit.
  • In response, it is noted that drift velocity is the relevant factor, influenced by applied voltage and resistance, affecting current flow in the circuit.
  • It is mentioned that higher resistance results in lower drift velocity and thus lower current for a fixed voltage source.

Areas of Agreement / Disagreement

Participants generally agree on the principle that current remains constant in a series circuit, but there are varying explanations regarding the effects of resistance and drift velocity, indicating some level of conceptual exploration and uncertainty.

Contextual Notes

The discussion does not resolve the complexities of how different resistances specifically affect current density or the precise mechanisms behind drift velocity changes in relation to resistance.

tasnim rahman
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How do resistors of different resistances in series maintain constant current throughout a circuit? I mean is not the current supposed to decrease (within the resistor only) while going through the resistors? Need quick reply.
 
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The total current flowing in a series circuit cannot change from one point to the next, since the current is conserved (the electrons don't flow out of the circuit). It is true that the total equivalent resistance of the circuit determines the current that a given voltage will output; but this current then flows through the circuit, equally through each individual resistor. What changes at each resistor is the voltage drop across it -- this is how a constant current is maintained.
 
Thanks a lot for the quick reply Bapowell. From the equation I=nAve, which one, the drift velocity or the electron density, is affected by resistors, for series circuit resistance? How does the input of a single resistor in a circuit reduce the whole current available in the circuit? Does current density have anything to do with it?
 
No problem, happy to help. In the expression I = nAve, the drift velocity is the quantity relevant to this discussion. The drift velocity is determined by the applied voltage, the constant of proportionality being the resistance. For a given voltage, say a 9 V battery, hooked up to series circuits with different equivalent resistances, we would find different currents flowing through each circuit, on account of the different drift velocities. Intuitively, this makes sense: the battery, or voltage source, pushes the electrons through the circuit. A 20V battery can push more electrons more easily than a 9V battery. Meanwhile, resistance impedes the flow of electrons, making it more difficult for the battery to push the electrons through the circuit. For a fixed battery, increasing the resistance of the circuit makes it more and more difficult for the battery to push the electrons, resulting in slower electron drift velocity, and hence, lower current.
 
Thanks a lot again. I think I got it now.
 

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