8
$\begingroup$

Why doesn't all the current flow down the path with the weaker resistance instead of dividing and going through both resistors (in a parallel setup with 2 unequal resistors)?

$\endgroup$
5
  • 3
    $\begingroup$ If ALL of the current went through one path, then the voltage drop across the larger resistor would be 0 (there's no current flowing through it). But this is a contradiction since 2 resistors in parallel are connected on each end by a wire (which ideally has 0 resistance), so the ends must be at the same voltage. Thus, the voltage drop across the larger resistor must the be the same as that across the smaller one. $\endgroup$ Nov 22 '15 at 5:27
  • 1
    $\begingroup$ You are taking it too literally. It is like water in parallel pipes. The larger pipe has less resistance to water flow. But not all the water goes through the larger pipe. The path of least resistance is for situations like touching a high voltage circuit - you'll get a shock if you provide a low resistance path to ground. It is not a technically precise description of the behavior though. You might use Ohm's law for that. $\endgroup$
    – mmesser314
    Nov 22 '15 at 6:24
  • 2
    $\begingroup$ Possible duplicate of How do electrons know which path to take in a circuit? $\endgroup$ Nov 22 '15 at 6:28
  • $\begingroup$ In practice there can be complications due to temperature effects. Power transistors sometimes consist of a number of parallel individual transistors. If there is current flowing through them they will heat up and their resistance goes down. Since they are not precisely equal some will get a lower resistance and conduct a larger current heating them up even more and lowering their resistance accordingly leading to a burnout. So measures are always taken to prevent this from happening. $\endgroup$
    – Urgje
    Nov 22 '15 at 14:35
  • $\begingroup$ A signal does NOT follow the path of least resistance. That statement implies there are multiple possible paths. The signal, at each instance of time, 'sees' ONE circuit which can depend upon whether the signal is constant (DC) or alternating (AC). $\endgroup$ Oct 29 '18 at 22:05
11
$\begingroup$

"Current takes the path of least resistance" is just a phrase people say but it's not totally accurate. When one path through the circuit has 0 resistance (a short), it is true that current follows that path only. It isn't true when you have multiple paths, with nonzero resistance, though. A better way of saying it would be "current flows through all paths in an amount inversely proportional to their resistance." This is basically just a fancy way of stating ohm's law.

$\endgroup$

Not the answer you're looking for? Browse other questions tagged or ask your own question.