Technical Question from Electrical Circuits 1

[DigilentStudio]

The following question was asked by a viewer on our Youtube channel. It is in response to Tim Hanshaw's Electrical Circiuts 1 lecture video.

 

Satnam Gill asked: how can you have current in two different directions in the same loop?

 

Thank you for taking the time to answer this question.

[JColvin]

Hi DigilentStudio and Satnam,

 

I presume that you're referring to what you can see on the screen behind Tim at around the 19 minute mark.

 

In the global sense when everything is turned on and flowing, you would not have current flowing in two different directions. However, when we are labeling polarities and current direction on a circuit diagram, we can orient them whichever way we want to as long as we remain consistent about which polarity current "flows into" (passive sign convention). Tim likes the orientation of having current flow into the + side of a component, so it looks like we have two different current directions based on what the problem originally gave us.

 

The trick to remember is that even though we labeled the current direction flowing one way, it does not mean that the current is forced to flow in that direction. Once we solve the problem, we might find (as is the case in this problem) the current is actually flowing in the opposite direction. This ends up giving one of the current arrows a positive current and the other current arrow a negative current (and consequently flipping the polarity on the component that has the negative current associated with it).

 

Let me know if you have any more questions.

 

Thanks,

JColvin