In a series circuit, the voltage is the same everywhere on that circuit. However, thinking about Voltage as a steady force or potential, I imagine that at parts of the circuit without resistance, the current would be greater as the force would be able to move them faster, without any obstruction. Why is this not the case?
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1$\begingroup$ No, the voltage is not the same everywhere. $\endgroup$– nasuCommented Dec 11, 2020 at 20:51
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$\begingroup$ I think you meant to say "In a series circuit, the current is the same....". Suggest you edit. $\endgroup$– Bob DCommented Dec 11, 2020 at 21:01
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5$\begingroup$ Does this answer your question? How does the current remain the same in a circuit? $\endgroup$– Bob DCommented Dec 11, 2020 at 21:05
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$\begingroup$ Each circuit element has its own voltage drop, including the wires running between circuit elements. And, the term "voltage" normally means voltage drop between circuit elements. $\endgroup$– David WhiteCommented Dec 11, 2020 at 21:24
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$\begingroup$ Re. "...current would be greater as the force would be able to move them faster..." Current has nothing to do with to the speed of the charge carriers (usually, electrons) in a circuit. Current is a measure of how many charge carriers pass a given point in a given amount of time. $\endgroup$– Solomon SlowCommented Dec 11, 2020 at 21:25
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2 Answers
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Voltage is not the same throughout all the elements in a series circuit. The sum of all the voltage drops across all the series elements is always equal to the source voltage.
The charge carriers flowing through a series circuit are conserved- there is nowhere else for them to go except in the circuit loop, and this means all the charge carriers exiting one circuit element enter the next one, and so on all the way around the complete circuit loop.
This means the current flowing through all the individual circuit elements in series is the same.
answered Dec 11, 2020 at 21:08
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The situation is completely analogous to that of a water pipe of uneven thickness (horizontal, so we can ignore gravity), with voltage being analogous to pressure. If the current through any part "tried" to increase (compared to the current in a neighboring part), it would create a buildup of charge (water molecule concentration in our pipe analogy), which would alter the voltage (pressure) gradient and make it slow down again.
For that reason a condition of unequal current can't persist for too long. Which means that in the normal, steady state situation (same current everywhere), the voltage (pressure) gradient varies along the path, to "enforce" the condition of the equal current in order to "compensate" for the fact that it's easier for the current to flow through some parts (low resistance/wider pipe) than through others.
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$\begingroup$ But the water does speed up in the narrower portions and still the flow rate is the same. I don't think using water analogy helps understanding electric circuits. Water flow is a lot more complicated and may be outside student's experience. $\endgroup$– nasuCommented Dec 11, 2020 at 21:54
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$\begingroup$ The same exact thing happens in narrower portions of the wire, which is the main reason I drew the analogy. $\endgroup$ Commented Dec 11, 2020 at 22:20
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$\begingroup$ There will be an accumulation of charge if the electrons did not speed up in the narrower section. Your answer suggest that the speedup is prevented by the same. Maybe I just did not understand your sentence properly. $\endgroup$– nasuCommented Dec 11, 2020 at 22:29
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$\begingroup$ Good point, I can see how my phrasing could cause confusion. I fixed it. $\endgroup$ Commented Dec 11, 2020 at 22:35