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This question has been asked before but I don't understand the answers to it. They say that by adding a resistor, it provides an additional path for current to flow and decreases the resistance. I understand how an additional path decreases resistance but how is adding another resistor adding an additional path? For example, say a parallel circuit branches off into two paths. You then add resistors to those two paths. How does that decrease the resistance? It isn't adding a new path?


marked as duplicate by Wesley Lee, helloworld922, Community May 22 '17 at 22:25

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • \$\begingroup\$ If you add a resistor in parallel, the current goes up. For the current to increase, the resistance must of decreased. \$\endgroup\$ – StainlessSteelRat May 22 '17 at 21:00
  • \$\begingroup\$ Why does the current go up if resistors slow down the flow of electrons? I understand that resistance decreases as current increases but I don't get the first part. \$\endgroup\$ – J. Doe May 22 '17 at 21:02
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    \$\begingroup\$ why can you get more cars down the road if you add more lanes? \$\endgroup\$ – old_timer May 22 '17 at 21:03
  • \$\begingroup\$ You have added a second path for electrons. \$\endgroup\$ – StainlessSteelRat May 22 '17 at 21:04
  • \$\begingroup\$ Oh okay sorry I misunderstood what you meant by adding a resistor in parallel. Thanks. \$\endgroup\$ – J. Doe May 22 '17 at 21:05

There's a waterfall pushing 600 gallons per second. You divert a small section through a small water hose giving you 5 gallons per second. Your current is 5 gallons per second.

Add another of the same size hose. You more have 2 currents that add up to 10 gallons per second.

It's like a single hose that does 10 gallons per second.

This is an approximation of how parallel resistors work.

  • \$\begingroup\$ +1. Just wanted to write the same stuff as analogy, but as you have answered this way, I will not do it :) \$\endgroup\$ – Anonymous May 22 '17 at 21:05

The second resistor is a second path for the current. Consider the following circuits:


simulate this circuit – Schematic created using CircuitLab

The first circuit, with V1, is your initial circuit. It's one volt across a one ohm resistor, with one amp of current. Next, you add a second one ohm resistor, as in the circuit with V2. Both resistors have one volt across them, so both resistors have one amp through them. That's just ohm's law. Since there are two resistors, that's a total of two amps coming from the source. The circuit connected to V3 shows an identical circuit from the source's point of view: one volt over half an ohm is two amps, just like with the two parallel resistors.


A parallel circuit decreases the resistance compared to a circuit where there are no parallel branches. Say you had 2 100 ohm resistors in parallel. Then you add a third 100 ohm resistor in parallel with the first two. Now the current has three path to go through compared to two, so it increases.

In the example you provided of adding resistors to a parallel circuit with no resistors initially, that would decrease current.

Adding parallel resistors only increases current if there was not initially a parallel branch at all.


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