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Suppose we have a very simple circuit, with just a resistor between a wire connected to a power source. What's the actual value of current travelling the wire before and after the resistor? Is it different? Or is it the same across the wire, between the power source?

My guess is that it should be the same, since the resistor limits the current flow, thus create a "congestion" for the current that goes through it. This congestion also slows down the current before entering the resistor and lessen the overall electrons flow through the wire because the resistor is limiting the total amount of electrons that can pass the resistor. So even if the wire can carry more electrons, but the resistor is limiting it, the wire only supplies the amount of electrons allowed by the resistor and the amount of electrons actually on the wire are the same as the maximum go through the resistor. Is this correct?

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    \$\begingroup\$ Don't analyze circuits by thinking of electrons moving in circles around a circuit. Electrons themselves physically traverse a DC circuit very slowly, and don't traverse an AC circuit at all (they just wiggle back and forth). Electrons that are moving move on the order of meters per hour (or slower) - what actually does the work in a circuit is the electromagnetic field which moves at nearly the speed of light from the source to the load. The electrons provide a path for the propagation of the energy, they aren't the energy itself. \$\endgroup\$ Mar 9 '14 at 1:56
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    \$\begingroup\$ Thanks. So, is electromagnetic field actually a current if it's not a movement of electrons from the surplus of charge point to deficiency point? \$\endgroup\$
    – Tu Do
    Mar 9 '14 at 7:31
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    \$\begingroup\$ amasci.com/elect/elefaq1.html#aelist \$\endgroup\$ Mar 9 '14 at 13:24
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Yes, the current in a wire leading up to a resistor will be the same as the current in the wire leaving the resistor (in the ideal case).

There are always real world factors that change ideal behavior however. There could be a small leakage current from the wires at near where they join the resistor or leakage from the resistor body itself to a surrounding part of the circuit. Leakage currents like this are normally exceedingly small and are thus usually ignored for most low voltage applications. They can however become much more significant in high voltage circuits.

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  • \$\begingroup\$ Thanks. And is it the same current as dictated by the resistor: the maximum current passed through a resistor? \$\endgroup\$
    – Tu Do
    Mar 8 '14 at 21:47
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    \$\begingroup\$ Yes. The resistor will always resist the current flow through it (afterall that is why it called a resistor). Keep in mind that wires are also not perfect and will have some resistance themselves and thus also limit the current to some extent. The degree to which the wire resistance will impact the resistor branch of the circuit will be in inverse proportion of the wire resistance versus the actual resistance in the resistor component itself. \$\endgroup\$ Mar 8 '14 at 21:51

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